Assign a line items currency as an attribute, not an option

core/app/models/spree/line_item.rb

@@ -104,15 +104,10 @@ def insufficient_stock?
     def options=(options = {})
       return unless options.present?
 
-      opts = options.dup # we will be deleting from the hash, so leave the caller's copy intact
+      self.price = variant.price_in(currency).amount +
+                   variant.price_modifier_amount_in(currency, options)
 
-      currency = opts.delete(:currency) || order.currency
-
-      self.currency = currency
-      self.price    = variant.price_in(currency).amount +
-        variant.price_modifier_amount_in(currency, opts)
-
-      assign_attributes opts
+      assign_attributes options.except(:currency)
     end
 
     private

core/app/models/spree/order_contents.rb

@@ -81,12 +81,14 @@ def add_to_line_item(variant, quantity, options = {})
 
       if line_item
         line_item.quantity += quantity.to_i
-        line_item.currency = currency unless currency.nil?
       else
-        opts = { currency: order.currency }.merge ActionController::Parameters.new(options).permit(PermittedAttributes.line_item_attributes).to_h
-        line_item = order.line_items.new(quantity: quantity,
-                                          variant: variant,
-                                          options: opts)
+        permitted_controller_parameters = ActionController::Parameters.new(options).permit(PermittedAttributes.line_item_attributes).to_h
+        line_item = order.line_items.new(
+          quantity: quantity,
+          variant: variant,
+          currency: order.currency,
+          options: permitted_controller_parameters
+        )
         create_order_stock_locations(line_item, options[:stock_location_quantities])
       end
       line_item.target_shipment = options[:shipment] if options.key? :shipment