Interesting indeed.
I have a theory that would probably explain the symptoms, but I admit I don't know how it happened.
It seems that you inserted the key without UAC elevation (are you logged on as an Administrator, or restricted user? Do you have UAC enabled or disabled? Did you get the UAC prompt when you were entering the key?)
Therefore, the system (e.g. the LOCALSYSTEM account where the services are running) can see only the original trial key - while the ordinary user account (where avast! GUI parts are running) see the new registration keys in their virtual copy.
I'd say... try to enter the (same) key again, and make sure you are logged on as an administrator before doing that.