run the attached example...
when the page is initially rendered with enough space the grid/listbox don't need a scrollbar

then reduce the browser height until a scrollbar appears in the grid/listbox
--> the column headers now contain a "column placeholder" for the space the native scrollbar will occupy OK

increase the browser height again until the scrollbars disappear
--> the "column placeholders" remain, causing mis-alignment of the real column headers with the cells below

Workaround

• set fixed height on the parent container of a grid or a listbox

  	<window border="normal" title="native" width="30%" height="350px">
  	    <custom-attributes org.zkoss.zul.nativebar="true"/>
  	    <div hflex="1" vflex="1">
  		    <grid vflex="1" hflex="1" >