SPA525 phones with fw 7.4.6 do not seem to resolve phone numbers into names using the phone's directory but use the call history instead. (It only searches the address book when it can't find the number in the call history.)
i.e.: A call comes in from a number that isn't in the phonebook and it is displayed on the phone's display. If one saves the number and assigns a name to it, phone will still only display the number on subsequent phone calls, until the call history is cleared. And even after that, it is not 100% reliable.
I have been able to replicate it on fw 7.4.5 as well.