I've had this issue on and off for a while now. Sometimes I've assumed it had to do w/ playback while its recording another event, because it's often unrepeatable upon rewind and I'm often watching the trail of a simultaneously recording show. It's also quite intermittent, which is befuddling, as I haven't been able to reliably predict it...but it happens.
I will say it presented itself shortly after one of the software updates. That's why I quietly 'lived w/ it'...hoping it would be resolved/fixed by a subsequent update. And, fortunately, I haven't noticed it as much lately, after the most recent software update.