Steps to Reproduce

run the attached example bugtreescrollbar_simple.zul

1) open "item-0"
2) select an item below e.g. "item-0-0-1"

Current Result

the scroll position changes unnecessarily
the scroll position even moves the selected item out of view

Expected Result

preserve the scroll position

Debug Info

this used to work in ZK 8.5.0 until the FL version 8.5.1.FL.20180131
from 8.5.1.FL.20180201 on the scroll position changes unexpectedly/incorrectly

only happens when the selection is updated from the server side

Root Cause

possible side effect of ZK-3835 ??
https://github.com/zkoss/zkcml/commit/4b8375285fabac5de1a8b8030cedf45f1ea4e641

Workaround

in many cases it it not necessary to update the selected item when the user selects an item via mouse click, avoid setting the selection directly and avoid binding selectedItem="@bind(vm.selectedItem)" use TreeModel.getSelection() instead