Comment 1 for bug 277199

After investigation, it appears the problem is with _isinstance(). It checks to see if cls is an instance of type (to distinguish between actual classes and ClassIDs). This is sufficient for new-style classes, but neglects to handle old-style classes properly because they are not of type type (they are ClassType).

Adding an additional check for type ClassType should fix the problem. Alternatively, we could negate the logic and check for type ClassID. The only "disadvantage" is that it would require users to use the ClassID class (which I think is already necessary anyway, in order for rules to be created properly).