I've got two systems currently running myth one backend and one frontend. Both are gentoo builds are running 2.6 kernels using the CVS versions of Myth and dvb-kernel. I did encounter something similar but that was to do with Suse's broken Qt build and a much earlier version of myth (somewhere around .11). It does work, I've currently got PiP working using channels from different muxes, which is cool.

I have to say, I hardly ever use rpms or packages, although I use the emerge function in gentoo. I'd recommend you download the sources for myth and IVTV and build them yourself.