It's very, very unlikely there was a driver regression between September and December, almost nothing changed in FreeBSD 7.0 between then. It's also highly unlikely any changes in the pfSense code base would have caused anything like that, since nothing at all related to Ethernet interface code has changed in a long time, longer ago than September.
Can you reliably replicate this being resolved going back to an earlier release, then breaking going back to 1.2.1 release? If so, what date is the one that works? Given the lack of changes in any related areas, I doubt if that's truly the case. If so, I have a bunch of 1.2.1 snapshots that I can make available to help narrow down further.