This was bugging me with fAPN too - mine would connect to my new MMS profile whenever searching for a connection. I did however follow the advice on here and by making a clone of my normal internet apn, the n900 now connects to the clone automatically. So this is definitely a workaround.

I did post on fMMS too as it would be handy for fMMS to be able to connect to the mms apn and then disconnect again after sending/receiving or after exiting the program. Do you think this is possible?