I don't have the UN60D8000, but I'll take a shot.
I assume you're using an HDMI interface. Perhaps it's losing the authentication (HDCP - which means copyright protection) and the cable box needs to reset the authorization. Do you see anything on the cable box's front panel, like "DVI" when this occurs?
OTOH, it shouldn't happen in the first place. Intermittent problems are tough to figure out, like is it only on one channel? That sort of thing.