That's a weird one. I suppose it's possible you had a partial blockage on the high side of the a/c system which limited the flow of liquid refrigerant to the expansion valve. I recently had this happend - the receiver/dryer clogged up. But I would never expect something like this to fix itself.
Most likely explanation is the heater valve (AKA monovalve) was leaking hot water through the heater core. The a/c and heater were fighting one another tooth and nail. When you shut the car down, the monovalve opens. When you restart the car, the monovalve closes again. Perhaps it got a good seating the second time?
The 124 monovalve is not rebuildable. However, it only takes a few minutes to disassemble and examine for any obvious problems. I was having some problems with sudden blasts of hot air on my 124. Taking apart the monovalve, staring at it for a while, and reassembling it seems to have cured the problem for now.