In DataGrid when hovering the column separator the mouse cursor changes to StrechCursor then when you start to drag and accidentally move out of the separator the mouse cursor used to change back to the regular cursor.
Now it does not. The change between 4.6 and 4.10 is :
protected function separator_rollOutHandler(event:GridEvent):void
The addition of the || resizeColumn ( no clue why it was added here)