listbox size conflict when using both vflex and rows

Steps to Reproduce

http://zkfiddle.org/sample/glef8/1-vflex-and-rows-on-listbox
resize the browser window

Current Result

the horizontal scrollbar (of the listbox) seems to disappear

Expected Result

consistent height, or error indicating incorrect usage

Debug Info

the listbox content gets recalculated to 640px pushing the scrollbar out of the visible listbox area

Root Cause

Workaround

don't use both rows and vflex="1" at the same time since both are used to determine the height