I have a similar problem with Kaffeine. I'm setting the dongle in DVB-T mode and trying to scan for channels. The program starts scanning, but it hangs at 12% or 22%, sometimes after 10-15 minutes goes farther and finds some senders and hangs again for the next 15 minutes. In many cases if the scan reaches 100%, the program freezes and can be only killed. I've waited for more than 30 minutes a few times with no effect.
By the way, how long does the full scan usually take? Are 40-60 minutes normal?