I installed the ChangeSet and ran the tests. They work as advertised.
I looked at the code as well and the use of allInstances bothers me slightly. As stated in the comment this is slow. However, as currently Behavior>>allSubclasses calls subclasses Behavior should get such a method. Either it should be subclassResponsibility if Behavior is supposed to be abstract.
Behavior is not abstract. In fact Behavior has been designed by deutsch and others because thy thought that people would be willing to create anonymous classes. For example CodA uses this trick to introduce meta-object transparently.
Is it? The class comment states the following: "I am a good starting point for providing instance-specific behavior (as in Metaclass)." Does that mean, it is not abstract? There are no instances of Behavior in my image. Has anyone used Behavior instances?
Read my joop paper on my web site to understand the point :).
The other possibility would be to move the ivar subclasses from Class to Behavior. This is how it is implemented in VAST 6.0.1, in Dolphin 5.1.3 and VWNC 7. I guess this might be a difficult change, though.
I'm not sure but this is true that changing the format of behavior can have ripple effect.
The method ClassDescription>>subclasses should be deleted.