Not sure if this is what you mean or the same, but have a look at this thread.http://talk.maemo.org/showthread.php?t=64784
Basically, numbers saved as a name, appear as the number if there are two instances of the same number saved, whether it be in the phone book or contacts saved in the email app. for example.
Hope that makes sense. Here's an example.
I had my dad's mobile saved in phone app as "dad", but also had his details saved in my hotmail contacts as " Peter" (his name), so the phone app doesn't know which name to use for that number, so uses neither. But as I say, I am not sure if this is what you meant the problem is.