document elements can't retrieve mouse down/up event when dragging layer

Summmary:

When using draggable plugin to enable the dragging feature on the layer, at the moment of dragging layer, the elements which register on document and listen to the mouse down event will not work.

Problem Desc:

http://groups.google.com/group/jquery-ui/browse_thread/thread/61297f6c2504eac9?hl=en

Root Cause:

The function mouseDown/mouseUp/mouseMove at the file ui.core.js will always return false, and then jQuery will stop the mouse event bubbling, that the elements register on document and listen to the mouse event will not works.

Impact:

All elements handlers which rely on the mouse down/up event will not work.