I get a similar problem, the game crashes if I do more than one session at a time (that means I can do P1 and quit, but if I try to do P1 + P2 or more, it freezes).
I hope CM can get their act together for PC in 2012, the little bugs with the PC version bother me.
Actually, you are right. My game crash only ever happens if I run any 2 sessions after each other. Start a new practice/qual/race no problem but change to anything else without first restarting the game and it will crash.