Normal Steps to reproduce
- run the zul with IE11
- select the first item
- click the down arrow icon several times on the bottom of the scrollbar to scroll down the tree
actual result
the tree enforces you to scroll back
expected result
users can scroll down normally
debug info
- 8.0.1 doesn't have such issue.
- if you keep pressing a mouse left button on the down arrow icon, it will scroll down as expected.
