I bumped into this issue twice while working page editor IE 8 support. Basically - when clicking the plus/edit buttons of the component bars in page editor, nothing happens.

The AJAX request is not made due to GWT's Scheduler.scheduleFinally(...) not executing the command. This would mean that the control is not returned to the browser loop for some reason. On the other hand - I failed to find anything that would capture the control.

All the pending requests are instantly sent to server once the mouse is moved out of the page editor iframe.