I just stumbled over this:

When you have a number assigned to multiple contacts an one of these contacts is calling you the N900 only shows the number.

Well, every other phone I had so far showed the either the most recent contact, the first/last matching.

When I remember correctly the N900 did the same prior to PR1.2

I don't know if you think in numbers or in names, I do the latter.

I know my mum and dad have both assigned the same land line number so if either of them shows up on my n900 I know it could be either mum or dad. When I see the number I first have to recognize it. In this case it might be easy cause you might now the number of you mum and dad pretty well.

There is a Bug and a possible solution for this behavior:
Show multiple contacts for a shared number instead of the number

Please vote for it if you like it.

Cheers
Bjoern