Bug: Concurrent mode processes state updates out of order

[sophiebits]

React version: 0.0.0-experimental-d7382b6c4

I have a sandbox that adds the next integer to an array every time you move your mouse: https://codesandbox.io/s/compassionate-currying-nccok.

Intermediate state updates get dropped, then come back later (eg: you would never expect it to render with [0, 2]):

My expectation is that these are all the same priority level and thus should get processed in order. Am I doing something wrong?

cc @acdlite @gaearon

[sophiebits]

Same issue with UserBlockingPriority: https://codesandbox.io/s/thirsty-neumann-x1wzx.

[sophiebits]

Diagnosis in #18538 (comment).

[gaearon]

Not sure if this is fixed for good but it doesn't repro on master.
https://codesandbox.io/s/youthful-gates-yq0jw