Finally got a response. Supposedly 1.75 could not have caused this problem (it was just a "daylight savings time update"). BUT, they are aware of the "skip back" problem and said that they should have a fix by mid June (next release for 721). For now, the rewind button is the temporary solution.
The email stated that the problem is being caused by some higher band channels...? One thing I did notice this weekend - it happens even with shows that are not recorded, but running live too, on some channels (I noticed it on channel 329).