I haven't posted to the list - I was waiting to see what kind of responses I got here first. For the time being I'm okay, I took down one of the firewalls.
What I think could be happening is, the dedicated carp link between the two machines may be a bad cable. Originally I didn't have spanning tree enabled on the bridges, because I wanted an instant failover, and the bridge would be down on the backup firewall anyway, so STP was pointless. So, if there was a bad cable, I could easily see the two servers fighting over who's master, and who's slave, since they would be talking over that dedicated link with a bad cable.
The ideal scenario is getting the hosting company to let me control .1, which I'm in the process of talking about with them. That would allow me to completely get rid of the bridge, and just use carp to handle .1 - done deal.
Anyway, thanks for the URL, I may set up a test environment just to check it out anyway.
By the way, if you're curious why this is such a huge deal to me, read http://forum.pfsense.org/index.php/topic,7668.0.html. We've doubled in size since then.