Dialogs always show first feedback message

In our project we have a dialog based on Hippo-ECM's AbstractDialog class, which is a wizard to create documents in the CMS tree. In this wizard, several different kinds of errors can error. If a user makes multiple errors, then the second and subsequent error messages are never shown. Instead, the first encountered error message remains visible. Somehow, the first error is cached indefinetely.

I don't know if this bug can reproduced in the Hippo ECM quickstart app. The best way would be to implement a simple dialog based on the AbstractDialog class with for example two buttons. Button 1 throws exception A, button 2 throws exception B. Then, to reproduce the bug:

1. click button 1
2. the message from exception A shows in the feedbackpanel
3. click button 2

actual:
the message for exception A shows in the feedbackpanel

expected:
the message for exception B shows in the feedbackpanel