I've tested the Retros at Spielberg Historic, at 100% race speed, and they do not spin out on exit of turn 2.
As far as I know, you should not need to do a full install - GSync should update the files, but to be double sure, you could delete your entire Retro folder and then run GSync, that way it will definitely renew every file relating to Retros.
I also tried a race start at the circuit, and they did the first few laps cleanly, no problems.