Delay after opening Datebox calendar during 3+ minutes work

After opening Datebox calendar there is few seconds delay when user works three or more minutes with Datebox. The delay only occurs in Internet Explorer 10 even in this simply zul page without viewmodel or template:

<?page title="new page title" contentType="text/html;charset=UTF-8"?>
<zk>
<window title="new page title" border="normal">
<datebox />
</window>
</zk>

Longer work with Datebox causes longer delay in calendar (10 or more seconds).