and the rest of you said, I stamped out of TL, walked across the bridge, asked for a 1 day pass and paid $10, they held my passport and got a receipt. Few hours later I came back and collected it, it had Myanmar stamps in and out.
Did it 2 months ago. Every thing went smoothly. Stamped out of thailand, got on a boat (50baht) , paid $10usd to get stamped in and out of myanmar,then spent a few hours in myanmar then then came back by boat (50baht). Then got a new thai 30 exempt stamp.
My confusion was caused from my assumption that it would be like the procedure at the ranong/Myanmar border: where they just stamped me in and out of myanmar at the same time and handed back my passport and left it to me to make sure I leave.