Trouble with Upload

Hi,

I recently started to use Vaadin and so far so good :D

I started to tweak the maven archtype application example (CRUD example).

The first showstopper:

I tried to add an Upload component to the ProductForm but the component stays in disabled state whatever I do :/
The same component is workingfine ifI put it onto Grid part (above the grid)
I inspect the element with chrome and the component is in disabled state and cannot be enabled... 
What can I do, and where can Isearch the cause?

​<form enctype="multipart/form-data" method="post" class="v-upload v-widget" id="gwt-uid-17" aria-labelledby="gwt-uid-16" action="http://localhost:8080/annotator-client/APP/UPLOAD/0/50/action/d64685e7-f0a2-42a8-886a-3b6893d43518"><div><input type="hidden"><input type="file" class="gwt-FileUpload" name="50_file" disabled=""><div tabindex="-1" role="button" class="v-button v-disabled" aria-disabled="true"><span class="v-button-wrap"><span class="v-button-caption">Upload</span></span></div></div></form>
 

I  find the cause :D
The gwt-FielUpload component is disabled if is off -screen.
So I need explicitly enabled every time when the form's  slide in is completed.