Paging Component shows wrong Page. Bug ?

<?page title="TestCase/Paging" contentType="text/html;charset=UTF-8"?>
<zk>
<window title="TestCase/Paging" border="normal" width="400px">
	<vbox>
		<button width="100px" label="Fill30" onClick="fill(30)" />
		<button width="100px" label="Fill20" onClick="fill(20)" />
		<grid id="tblDemo" fixedLayout="true" onCreate="self.setPaginal(pg)" pagingPosition="bottom" width="300px" height="400px"  mold="paging" > 	 
			<columns>
				<column id="tblDemoCol1" label="Number" width="280px"/>
			</columns>
			<rows></rows>
		</grid>
		<paging id="pg" autohide="true" pageSize="10" detailed="true"/>
	</vbox>
	
	<zscript language="Java"><![CDATA[
		 void fill(int nCount){
			 clearGrid(tblDemo);
			 
			 Rows rows = tblDemo.getRows();
			 
			 for (int i = 0; i<nCount; i++){
				 Row row = new Row();
		
				 Label l = new Label(Integer.toString(i));
				 row.appendChild(l);
				 rows.appendChild(row);
			 }
		 }
	 
		public void clearGrid(Grid grid){
			 Rows rows = grid.getRows();
			 List myList = rows.getChildren();
			 int y = myList.size();
			 for(int f=y-1 ; f>=0 ; f--){
				 AbstractComponent comp = (AbstractComponent)myList.get(f);
				 rows.removeChild(comp);	
			}
		}
	
	 ]]>
	</zscript>
</window>
</zk>