It’s been a long time since I worked with BetaSP, but I think the problem is this. Beta records timecode in two places – VITC and the audio time-code track, and right now they don’t agree. When the tape is moving at normal speed, the deck is reading audio timecode. When the tape is slow or still, the deck reads VITC, and you’re seeing the discrepancy. There should be a switch that tells the deck to read time code as Auto, VITC or audio. You’re in auto now, so it switches to VITC when you stop the tape, and the deck is confused. The quick fix is to force the deck to read audio TC only, but if you re-black the head of the tape the VITC and audio timecode should agree and the problem will go away.
Hope that helps.