upload button doesn't work in second tabpanel

Question

i think it is bug but i am not sure maybe i did sth wrong.

PS. if you know how change it and keep the functionality and visibility, please let me know

<?page title="Preumowa" contentType="text/html;charset=UTF-8"?>
<zk>
<window id="mainWindow"  border="normal"    apply="org.zkoss.bind.BindComposer">
  <button label="works" upload="true,maxsize=50000, multiple=true, native"  onUpload="@command('addDocument',typDokumentu='PU')"/>  
  <tabbox>
    <tabs>
        <tab label="tab1"/>
        <tab label="tab2"/>
    </tabs>
    <tabpanels>     
        <tabpanel>          
            <button label="works" upload="true,maxsize=50000, multiple=true, native"    onUpload="@command('addDocument',typDokumentu='PU')"/>              
        </tabpanel>

        <tabpanel>
            <button label="doesn't work" upload="true,maxsize=50000, multiple=true, native"     onUpload="@command('addDocument',typDokumentu='PU')"/>                              
        </tabpanel> 
    </tabpanels>
  </tabbox>
</window>
</zk>

Answer 1

This was/is a bug in zk.

You have already created a bug tracker for it.
This is the original bug tracker.

Here is a zk fiddle with your code, strangly enough it works on the fiddle.