Comment #1 on issue 2928 by luc.fabresse: Trying to change the category of traits method -> DNU http://code.google.com/p/pharo/issues/detail?id=2928 I tried to move a method from one protocol to another and it works perfectly. But I tried to add a new protocol on a trait and it produces a DNU. This bug comes from a UI bug. TraitBehavior>>allSuperclasses return an empty collection. and creating a requestFormWindow with empty collections through a DNU because it is not checked in PopupChoiceOrRequestDialogWindow>>handlesKeyboard: Try this : UIManager default chooseOrRequestFrom: #() lines: #() title: 'Test Empty'. I attached a really silly patch. I am sure that there is something better to do. Attachments: PopupChoiceDialogWindow.LucFabresse.1.cs 898 bytes