If I understand correctly, the deck is flipping the cassette before it has reached the end.
I would hazard a guess that there is a mechanism which reacts to the resistance of the tape as it is pulled off the supply wheel by the transport. When the force required to do this is too great, the deck thinks the tape has reached the end and needs to be flipped.
Some possible causes of a malfunction here might be an overtight cassette, a worn or slipping drive belt or a weak motor.
If you are getting the problem even with cassettes you know are normal, I would say it's time to take the deck in to a Nak-savvy shop.
I would hazard a guess that there is a mechanism which reacts to the resistance of the tape as it is pulled off the supply wheel by the transport. When the force required to do this is too great, the deck thinks the tape has reached the end and needs to be flipped.
Some possible causes of a malfunction here might be an overtight cassette, a worn or slipping drive belt or a weak motor.
If you are getting the problem even with cassettes you know are normal, I would say it's time to take the deck in to a Nak-savvy shop.