Dialog Draggable Bug

Example http://jqueryui.com/dialog/#modal-confirmation

For view Bug Need get in body and create scroll.

1. Get Example in new window and add more textlines in BODY.

2. Minimised window browser that vertical scroll enabled.

3. Hand move scrollbar anymore as something.

4. Try move Dialog.... dialog window change position from cursor to another place..

I'm record video this bug, it's easy for understanding!

1. prepare for bug: https://dl.dropboxusercontent.com/u/15284528/V_20140403_123113.mp4

2. view bug: https://dl.dropboxusercontent.com/u/15284528/V_20140403_123201.mp4

snx.