What ways can families be used?

I just posted a bug to the tracker about families. Currently if your family already has just a sprite with the rts behavior, then you add another sprite with the rts, and bones behavior it will cause an error runtime.

My question is was this meant to be doable? I know its automatically a bug because of the crash, but Im getting other strange things to happen when i mix sprites with various behaviors.

The wiki says its used with objects of the same plugin type, but it says nothing about behaviors, or if it can be used with other families.

Behaviors (and effects) are supposed to work on the same principle as private variables. If all the types in the family have variables, behaviors or effects in common, they appear in the family as well. So ideally it would work with any combination of objects with behaviors - the ones in common to all of them appear in the family.