The T4 timeout oddity, as well as the "Offline" modem status being shown when the connection is fully 100% working, are known 1.0.6.6 firmware bugs. It's been discussed pretty heavily over on the official Comcast forums. Possibly 1.0.6.8 fixes these -- I need release notes before I can say.
Thank you. I don't see the specific bugs mentioned, but it may be possible that in the 2nd bulletpoint of section 8.1.2 they re-worked the logic surrounding that code thus fixed the underlying bugs. I'll let folks know if/when the time comes.