[martinced]

Multiple registration of callbacks and "too many similar events firing" (and even circular event firing : event A triggers event B, event B triggers event A) can all be solved by using event filtering no!?

I'm not saying it's a good thing to work around the issue by using event filtering, but events filtering is a great technique.

You can also use your event filtering to "fail fast" during development: detect a duplicated event called back? Throw an exception / make your application fail.