Just another update here… it seems that whatever the problem was with the cards has mysteriously ceased.
I started 20 torrents with the biggest dvd iso's of linux I could find and whatever else that was big enough to kill my connection for the night, reboot pfSense, and went to bed. 10 on the LAN subnet (sis1) and 10 on the OPT1 subnet (sis0). Also had music streaming from opt1 to LAN, and wrote a simple batch file to constantly send an iso 'the ultimate boot cd' back and forth across the connections.
So far, it doesn't seem like the error has cropped up anymore. I'm guessing once the 'short cable fix' is set, it works from then on, even across reboots? I don't see any more of that message other than the ones right after the cards are initialized.
Odd thing is that before re-formatting and installing pfSense 1.2.3RC1 from the ISO instead of 1.01>updated to 1.2.3RC1, I saw this message at least 5 times an hour. Clean install FTW?
confused.