This has started happening to me recently and it always seems to be because the next scheduled recording is in the past. It has somehow reappeared despite already having been completed.
Today, for instance, I noticed the hard disk was staying active when I switched it to standby, as if it was waiting to start an imminent recording. When I switched it on and looked at the schedule, the next scheduled recording was last night's Only Connect, which had already been recorded, watched and deleted. I had to delete the series schedule and add it again from next week's episode to get the box to go into full standby.
This has happened a few times lately with different recordings and I'm sure it only started recently. What could have changed?