Multiple assertions on the same rule set

I've written a test (that fails) to explain what I mean, but I can't work out whether this is a bug or intended behaviour?

I often want to add two allow rules with the same role, resource and privilege settings but different assertions. When doing this, the second allow rule always overwrites the first.

Am I doing it wrong, or should the Acl keep both rules? I can work around this by implementing a "MultiAssertion" class, or perhaps grouping things better, but happy to attempt a fix if anyone agrees?