diff --git a/devtools/visual-testing/tests/interactions/stories/formatting/clear-format-undo.ts b/devtools/visual-testing/tests/interactions/stories/formatting/clear-format-undo.ts
new file mode 100644
index 0000000000..c75ba72dbb
--- /dev/null
+++ b/devtools/visual-testing/tests/interactions/stories/formatting/clear-format-undo.ts
@@ -0,0 +1,59 @@
+import { defineStory } from '@superdoc-testing/helpers';
+
+const WAIT_MS = 300;
+const FONT_NAME = 'Courier New';
+
+export default defineStory({
+  name: 'clear-format-undo',
+  description: 'Clear formatting on styled text, then undo to verify marks are fully restored.',
+  tickets: ['SD-1771'],
+  startDocument: null,
+  layout: true,
+  toolbar: 'full',
+  waitForFonts: true,
+
+  async run(_page, helpers): Promise<void> {
+    const { step, type, newLine, bold, italic, selectAll, undo, focus, executeCommand, waitForStable, milestone } =
+      helpers;
+
+    await step('Type and format text', async () => {
+      await focus();
+
+      // Type three lines with different formatting
+      await bold();
+      await type('Bold text here.');
+      await bold();
+      await newLine();
+
+      await italic();
+      await type('Italic text here.');
+      await italic();
+      await newLine();
+
+      await type('Custom font text.');
+      await waitForStable(WAIT_MS);
+
+      // Apply a custom font to the last line
+      await selectAll();
+      await executeCommand('setFontFamily', FONT_NAME);
+      await waitForStable(WAIT_MS);
+
+      await milestone('formatted', 'Text with bold, italic, and Courier New applied.');
+    });
+
+    await step('Clear formatting', async () => {
+      await selectAll();
+      await executeCommand('clearFormat');
+      await waitForStable(WAIT_MS);
+
+      await milestone('cleared', 'All formatting cleared from text.');
+    });
+
+    await step('Undo clear format', async () => {
+      await undo();
+      await waitForStable(WAIT_MS);
+
+      await milestone('after-undo', 'Undo restored formatting — bold, italic, and Courier New should reappear.');
+    });
+  },
+});
diff --git a/packages/super-editor/src/core/commands/unsetAllMarks.js b/packages/super-editor/src/core/commands/unsetAllMarks.js
index ba9cc2b9dc..8f02995acb 100644
--- a/packages/super-editor/src/core/commands/unsetAllMarks.js
+++ b/packages/super-editor/src/core/commands/unsetAllMarks.js
@@ -1,5 +1,14 @@
 /**
  * Remove all marks in the current selection.
+ *
+ * We collect marks only from leaf/atom nodes (text nodes) and remove each
+ * explicitly via `tr.removeMark(from, to, mark)`.  This avoids a ProseMirror
+ * asymmetry: `RemoveMarkStep` strips marks from ALL inline nodes (including
+ * non-atom containers like `run`), but its inverse `AddMarkStep` only adds
+ * marks to atom nodes.  When a container carries a mark with different attrs
+ * (e.g. textStyle with all-null attrs on a run node), undo would overwrite
+ * the correct mark on the text node.  By scoping removal to leaf-node marks
+ * only, the undo path restores the exact marks that were visible to the user.
  */
 //prettier-ignore
 export const unsetAllMarks = () => ({ tr, dispatch, editor }) => {
@@ -12,7 +21,26 @@ export const unsetAllMarks = () => ({ tr, dispatch, editor }) => {
   if (dispatch) {
     if (!empty) {
       ranges.forEach((range) => {
-        tr.removeMark(range.$from.pos, range.$to.pos);
+        const from = range.$from.pos;
+        const to = range.$to.pos;
+
+        // Collect unique marks from leaf/atom nodes only (not inline containers)
+        const seen = new Set();
+        const marksToRemove = [];
+        tr.doc.nodesBetween(from, to, (node) => {
+          if (!node.isInline || !node.isLeaf) return;
+          for (const mark of node.marks) {
+            const key = mark.type.name + '\0' + JSON.stringify(mark.attrs);
+            if (!seen.has(key)) {
+              seen.add(key);
+              marksToRemove.push(mark);
+            }
+          }
+        });
+
+        for (const mark of marksToRemove) {
+          tr.removeMark(from, to, mark);
+        }
       });
     }
     // Clear stored marks to prevent formatting from being inherited by newly typed content
diff --git a/packages/super-editor/src/extensions/format-commands/clear-format-undo.test.js b/packages/super-editor/src/extensions/format-commands/clear-format-undo.test.js
new file mode 100644
index 0000000000..8a004baa52
--- /dev/null
+++ b/packages/super-editor/src/extensions/format-commands/clear-format-undo.test.js
@@ -0,0 +1,127 @@
+import { describe, expect, it } from 'vitest';
+import { TextSelection } from 'prosemirror-state';
+import { initTestEditor, loadTestDataForEditorTests } from '@tests/helpers/helpers.js';
+
+/**
+ * SD-1771: Formatting - Undo clear formatting leaves mixed formatting
+ *
+ * Root cause: run nodes (non-atom inline containers) can carry a textStyle
+ * mark with all-null attrs.  ProseMirror's `tr.removeMark(from, to)` creates
+ * RemoveMarkStep for marks on ALL inline nodes (including the run's
+ * null-attrs textStyle).  On undo, AddMarkStep only applies to atom/text
+ * nodes, so the run's null-attrs textStyle overwrites the text's correct
+ * textStyle mark.
+ *
+ * Fix: unsetAllMarks now collects marks only from leaf/atom nodes and removes
+ * each explicitly, avoiding RemoveMarkSteps for container-node marks.
+ */
+describe('SD-1771: Clear format + undo mark restoration', () => {
+  it('should restore textStyle mark attrs after clear format + undo (simple doc)', () => {
+    const { editor } = initTestEditor({
+      loadFromSchema: true,
+      content: {
+        type: 'doc',
+        content: [
+          {
+            type: 'paragraph',
+            content: [
+              {
+                type: 'run',
+                attrs: {
+                  runProperties: {
+                    bold: true,
+                    fontFamily: { ascii: 'Roboto', hAnsi: 'Roboto', cs: 'Roboto' },
+                    fontSize: 44,
+                    color: { val: '000000' },
+                  },
+                },
+                content: [
+                  {
+                    type: 'text',
+                    text: 'Hello World',
+                    marks: [
+                      { type: 'bold' },
+                      {
+                        type: 'textStyle',
+                        attrs: { color: '#000000', fontFamily: 'Roboto, sans-serif', fontSize: '22pt' },
+                      },
+                    ],
+                  },
+                ],
+              },
+            ],
+          },
+        ],
+      },
+    });
+
+    const from = 2;
+    const to = 2 + 'Hello World'.length;
+    editor.view.dispatch(editor.state.tr.setSelection(TextSelection.create(editor.state.doc, from, to)));
+    editor.commands.clearFormat();
+    editor.commands.undo();
+
+    const marks = [];
+    editor.state.doc.descendants((node) => {
+      if (node.isText) marks.push(...node.marks.map((m) => ({ type: m.type.name, attrs: { ...m.attrs } })));
+    });
+    const textStyle = marks.find((m) => m.type === 'textStyle');
+    expect(textStyle).toBeDefined();
+    expect(textStyle.attrs.color).toBe('#000000');
+    expect(textStyle.attrs.fontFamily).toBe('Roboto, sans-serif');
+    expect(textStyle.attrs.fontSize).toBe('22pt');
+  });
+
+  it('should restore textStyle marks correctly after clear format + undo (real DOCX)', async () => {
+    const { docx, media, mediaFiles, fonts } = await loadTestDataForEditorTests('sdpr.docx');
+    const { editor } = initTestEditor({ content: docx, media, mediaFiles, fonts });
+
+    // Find first paragraph with styled text (textStyle marks with real values)
+    let targetFrom = null;
+    let targetTo = null;
+    let expectedColor = null;
+    let expectedFontFamily = null;
+    let expectedFontSize = null;
+
+    editor.state.doc.descendants((node, pos) => {
+      if (targetFrom !== null) return false;
+      if (node.type.name === 'paragraph' && node.textContent.length > 5) {
+        node.descendants((child) => {
+          if (targetFrom !== null) return false;
+          if (child.isText) {
+            const ts = child.marks.find((m) => m.type.name === 'textStyle');
+            if (ts && (ts.attrs.fontFamily || ts.attrs.fontSize || ts.attrs.color)) {
+              targetFrom = pos + 1;
+              targetTo = pos + node.nodeSize - 1;
+              expectedColor = ts.attrs.color;
+              expectedFontFamily = ts.attrs.fontFamily;
+              expectedFontSize = ts.attrs.fontSize;
+              return false;
+            }
+          }
+        });
+      }
+    });
+
+    expect(targetFrom).not.toBeNull();
+
+    editor.view.dispatch(editor.state.tr.setSelection(TextSelection.create(editor.state.doc, targetFrom, targetTo)));
+
+    // Clear formatting then undo
+    editor.commands.clearFormat();
+    editor.commands.undo();
+
+    // After undo, the first text node's textStyle should have the original attrs
+    let textStyleAfterUndo = null;
+    editor.state.doc.nodesBetween(targetFrom, Math.min(targetTo, editor.state.doc.content.size), (node) => {
+      if (!textStyleAfterUndo && node.isText) {
+        textStyleAfterUndo = node.marks.find((m) => m.type.name === 'textStyle');
+      }
+    });
+
+    expect(textStyleAfterUndo).toBeDefined();
+    expect(textStyleAfterUndo.attrs.color).toBe(expectedColor);
+    expect(textStyleAfterUndo.attrs.fontFamily).toBe(expectedFontFamily);
+    expect(textStyleAfterUndo.attrs.fontSize).toBe(expectedFontSize);
+  });
+});
diff --git a/packages/super-editor/src/tests/data/sdpr.docx b/packages/super-editor/src/tests/data/sdpr.docx
new file mode 100644
index 0000000000..b3b56b8fda
Binary files /dev/null and b/packages/super-editor/src/tests/data/sdpr.docx differ