tree scroll pos + latency errors

Steps to Reproduce

run the attachment tree-scroll-latency-issues.zul

refresh the page
click either button
-> a sequence of timed scroll position updates is replayed

Current Result

after clicking button "remains blank"
-> no tree item visible at the current scroll position
-> tree items are rendered somewhere else outside the current view

after clicking button "jumps to bottom"
-> after the sequence the scroll position jumps to the bottom of the tree

Expected Result

• after updating the scroll positions the tree should render the items visible for this position
• no scroll jumps

Debug Information

the buttons simulate a sequence of scroll position updates to get consistent test results, and simulate server side latency (otherwise it's difficult to reproduce this reliably, still it is possible to get these results under certain latency and specific mouse wheel/drag movements)

Workaround