The progress dialog opens a very big window and does not update.
This only happens when the cache has been cleared (in FF 4.0 & 3.6.16)
1. Clear the cache
2. Load the window examples: http://dev.sencha.com/deploy/ext-4.0...x/msg-box.html
3. Press the Show button for the progress dialog.
I am getting similar errors in my application that is using a progress bar dialog.