Steps to Reproduce

run the attached example grouplist-invalidate-scrollpos.zul or grouplist-open-group-scroll.zul

1. scroll to the bottom of the listbox
2. close/open the last group

-> in both cases the second last group will close automatically

Current Result

the scroll vertical scrollbar size is inconsistent with the content height

Expected Result

consistent scrollheight matching the content height

Debug Info

in both cases this happens due to combined onOpen and invalidate
in grouplist-invalidate-scrollpos.zul invalidate() is called explicitly
in grouplist-open-group-scroll.zul invalidate is causes because more than 10 listitems get removed when closing "group 3", trying the same with "group 2" doesn't cause the problem

Workaround

increasing the invalidateThreshold can avoid the issue

(commented out in grouplist-open-group-scroll.zul)