ZK-2551 regressions in mobile

<zk>
  <window border="normal" title="hello" >
    	<vbox>
            <label multiline="true">
                1. scroll to the far right in the listbox
                2. click the button to fire CONTENTS_CHANGED fro first item in model
                3. the horizontal scroll bar shouldn't scroll to the leftmost of the listbox
            </label>
    ROD false
  	<listbox id="lb" mold="paging" width="300px" height="200px" >	
  	<custom-attributes org.zkoss.zul.listbox.rod="false"/>
          <listhead>
            <listheader id="listheader2" label="col2" width="350px"/>            
            <listheader id="listheader1" label="col1" hflex="min"/>
          </listhead>
          <template name="model">
          	<listitem>
          		<listcell>${each}</listcell>
          		<listcell>${each}</listcell>
          	</listitem>
          </template>
    	</listbox>
	<button id="btn" label="Click to fire CONTENTS_CHANGED for first item in model." onClick="changeModel()"/>
  <zscript><![CDATA[
	ListModelList model = new ListModelList();
	model.add("a");
	model.add("b");
	lb.setModel(model);
	public void changeModel() {
		model.set(1, "replaced");
	}
]]></zscript>
  </vbox>
  </window>
</zk>