Mouse events are not sent when the nodes under the mouse change during layout. This then represents an incorrect state in that the hover state of where the mouse actually doesn't match the current hover state of the document. To fix a variety of issues we will start dispatching mouse transitional events and update the hover state shortly after layout has been executed. This will match Firefox behavior.
Docs: https://docs.google.com/document/d/1TgqvDg8L_TkEiNjBUaz39FDgxpp5aj9ZdIWeQSanKHY/edit
Samples: http://jsfiddle.net/mrwb605v/5/ http://jsfiddle.net/Uf3xQ/25/