Problem submitting a form in window with contrainHeader set to true

Hi,

I had my application set up so that this was called in my launch method:

Code:

        Ext.override(Ext.Window, {
            constrainHeader:true
        });

Popup windows are used containing forms but when submit is called it generates an error in Panel.js:2320 (calculateConstrainedPosition) where the me.header.lastBox is undefined.

Regards,

Paul