Steps to Reproduce

run the attached example grouplist-focus-position.zul

A (broken case)
1) scroll down
2) check "item 2-5"
3) scroll up
4) collapse "group 2"

B (working case)
1) scroll down
2) check "item 2-1"
3) scroll up
4) collapse "group 2"

Current Result

in case A the vertical scrollbar remains even though all collapsed groups fit into the scrollable area
where in case B the scrollbar disappears as expected

Expected Result

In both cases A and B the scroll bar should disappear

Root Cause

in case A the hidden focus-a keeps its css-top position causing the scrollable area to extended showing an unnecessary scrollbar

Workaround

focussing the group item when during onOpen fixes the focus anchor position

<listgroup id="group2" label="group 2" open="true" onOpen="self.focus()"/>