You need to re-boot. Sounds like its confused. I record OTA, cable channel and watch something I recorderd-all at the same time. If a reboot doesn't fix it, you need to call dish. Maybe the unit is broken.
happened last week, i rebooted the other day, and it happened again recording 24 last night. the reboot was because timers were not firing, thats fixed now.
If you do a manual record (press record button) then you cannot switch away it seems. Prehaps this is because it expects you to manually stop it. If you do a timed record there should not be a problem.
-Ken