When resizing a listbox column so the other columns get pushed out of the viewport, no horizontal scrollbar is displayed if the listbox is empty.
Example: http://zkfiddle.org/sample/1oqj1ro/2-Listbox-sorting-header-shifting#source-1 (you have to empty the ListModel in the ViewModel first)

Also, in ZK 7 there seems to be a weird behavior in this situation. Depending on what item is hovered, a scrollbar appears or vanishes.