This has been happening to me with SD recordings only for about a month or two now. Sometimes the skip back button works properly but most of the time it does not. I have the same exact problem with the skip back button going back a second or two and then many minutes. Sometimes with just one press it goes back a few minutes. Also when using the fast forward button and pressing play to stop somewhere, it stops about 5-10 seconds after what was on the screen when you pressed play. This always happens at every fast forward speed except for x4. I haven't noticed a problem with skip forward, however I don't use it often.
And while we're talking about DVR problems. Whenever two recordings start at the same exact time one of them always has a black screen and no sound for about 10 seconds. Also if you are fast forwarding or rewinding and a timer is just about to start it will not start and will freeze the receiver in the fast forwarding or rewinding mode until either it reaches the end or beginning of the program. Though sometimes after a few seconds or almost a minute it will stop the fast forwarding or rewinding and record the program. It seems to be random when the freezing decides to stop, but it always happens.