I'm new with the 3416 and YES, I noticed the phenomenon 2 days ago. I cannot say for sure whether it was an NBC/GE channel I was watching...I'll check tonight but I DID determine that the flip to the end of the recording required several seconds to "activate." Thus I've been using the high speed FF (3 clicks) and spinning through a commercial bevy to a count of 8, the first three counts of the 8 are the three pushes of the FF button. Any slower speed FF takes too long and triggers the flip.
My silly method goes fast enough so as not to trigger the unwanted end of the recording.
I have my own reason for not wanting Comast to buzz my set or send a repairman.
I notice there's no corresponding problem with FAST REWIND so if I overshoot with FAST FF I can go backwars slowly.
(P.S., Is the 3416 a very new model?)