Steps to Reproduce

run the attached example
click one of the buttons (1) before and (2) after moving the horizontal scrollbar

Actual Result

(1) the new listheader (listcells) is displayed properly but the frozen scrollbar is out of synch
(2) the new listheader (listcells) don't become visible at all

Expected Result

adding listheaders/listcells should display and update the frozen component/scrollbar

Workaround

calling listbox.invalidate() after adding the listheader/cells on will rerender correctly