Bandbox, Form Binding and Constraints with Chromium and (less reprodible) Firefox

Me again.
I face an issue with Bandbox used in a MVVM form with a "no empty" constraint.
How to reproduce:

• Open page
• Press at first save - the standard "no empty" error popup appears
• Select an item in the bandbox
• Press save again - popup appears again

First I saw that with Firefox. Now with simplifying the example it appears less and less often, sometimes only in debugger.
Then I tried with Chrome and there it always happens.

The reason seems to be an ErrorEvent which is still sent by the client.
I hope you also see that behavior.