scrollbar will jump back after scroll to bottom-most position

Steps to reproduce

1. run attached zul
2. drag scrollbar to bottom-most position
   if in 7.0.1, move cursor out of listbox immediately to make scrollbar disappear
3. drag scrollbar to top-most position
   if in 7.0.1, move cursor out of listbox immediately to make scrollbar disappear
4. repeat 2
   Customers also reported that sometimes scrollbar freezes when dragging with IE.
5. if in 7.0.1, hover mouse on listbox to see scrollbar position

Actual Result

Scrollbar is not at the bottom-most position.

Expected Result

Scrollbar is at the bottom-most position as I scrolled.

Extra Information

also can reproduce it in 7.0.3.FL.20140806-Eval