I ran an HDHomeRun under beta3 for almost 3 months... running it under RC1 at the moment, again, no problems. You may want to check the compatibility of your cable connection, perhaps a modulation difference?
I use HDHomeRun to pull OTA ATSC, but I have successfully used it to pull the QAM256 off of Comcast cable (they do nasty things to the PSIP though, so channel #s are always fun to decode) :-P
-Thom