No help on the resetting settings. HDMI is supposed to work with a handshaking protocol between the source (your cable box) and the destination (your TV). In this handshaking procedure, the source asks the destination what it is and what resolution it is capable of, and they two devices negotiate to determine what format to send things in (if sending it at all, some HDMI sources will refuse to send to a destination which they think might copy the material). My guess is that the DVI-HDMI conversion is confusing the TV, and it is trying to accommodate itself to what it sees as a confused source of data. You probably don't have the option, but an HDMI out cable box may work better.
Although I work as an engineer in the video industry (semiconductor), the consumer electronics side of things is relatively new to me. I just put in my first HT system and have been amazed by it (TX-SR705, Panasonic DMP-BD30 Blu-Ray player, TH42PZ700 TV, and SA 8300HD cable box, all connected via HDMI)