steps to reproduce

1. load the zul below

   <zk>
   	<zscript><![CDATA[
   		ListModelList items = new ListModelList();
   	    for(int i = 0; i <= 250; i++) {	    	
   	    	String label = "Item "+i;	    	
   	    	items.add(label);
   	    }
   	   //items.setMultiple(true);
   	   
   	   ListitemRenderer renderer = new ListitemRenderer(){
   	   	void render(Listitem item, Object data, int index){
   	   		item.appendChild(new Listcell());
   	   		Listcell cell = new Listcell();
   	   		Label label = new Label((String)data);
   	   		label.setMultiline(true);
   	   		label.setParent(cell);	   		
   	   		item.appendChild(cell);
   	   	}
   	   };
   	]]></zscript>
   	<borderlayout>
   		<center>
   			<listbox hflex="1" id="theListbox"  onPaging="self.focus()" mold="paging" pageSize="100" height="400px" pagingPosition="bottom" checkmark="true" multiple="true" model="${items}" itemRenderer="${renderer}">
   				<custom-attributes org.zkoss.zul.listbox.rod="true"/> 
   				<listhead>
   					<listheader/>
   					<listheader label="col"/>
   				</listhead>				
   			</listbox>
   		</center>
   	</borderlayout>
   </zk>
   

   or http://zkfiddle.org/sample/2n0dcer/3-empty-like-listbox

2. scroll to show the last item in the 1st page
3. go to the last page by clicking the paging control

result

an empty-like listbox, but there are actually 50 items.

The scrollbar position is incorrect.

Debug info

1. remove onPaging="self.focus()" and this issue doesn't happen.
2. After the issue happens, selecting an item will eliminate the issue.
3. 7.0.0 ~ 7.0.4 don't have such issue.
4. When the issue happen, z-focus-a's top position is too large, it should be 1555px
   <button id="d4KQ2-a" style="top: 2776px; left: 0px;" onclick="return false;" href="javascript:;" class="z-focus-a"></button>

Workaround

• (for 6.5.8.1) do not maintain scrolling position

  	<script><![CDATA[
  zk.afterLoad('zul.sel', function() {
  	var old = {};
  	zk.override(zul.sel.SelectWidget.prototype, old, {	                 
  		focus_: function (timeout) {
  			var btn;
  			if (btn = this.$n('a')) {
  				if (this._focusItem) {
  					for (var it = this.getBodyWidgetIterator(), w; (w = it.next());) 
  						if (this._isFocus(w)) {
  							w.focus_(timeout);
  							break;
  						}
  				}
  				this.focusA_(btn, timeout);
  				return true;
  			}
  			return false;
  		}
  	});
  });
  	]]>
  	</script>