fast forward DVR , HR54-700

I have noted on some programs I record the fast forward function does not work correct, it works, odd like?  It FF's but you don't see it on the screen, instead you are in the dark as to where you are at in program until you go back into play, the picture just stays frozen where you left it.  How come it does this?  It happens very occasionally and when it does, it does not do it on any particular show or channel.  The bottom indicator kind of "jumps" forward in chucks as this happens.  I have the HR54-700 receiver. Most of the times the DVR records & FF's correctly.

I have reset the receiver.

Al