I actually ran into a problem with my Carvex that eventually required service. After a month or so of using it the blade was all of a sudden out of square -- no precipitating event, such as dropping it or making an overly aggressive bevel cut. Talked to Festool on the phone and they told me to try and realign it by using the star screw. After putting it back into square using this method it didn't take long before it was again out of square. After examining it very closely, I realized that there was a small amount of play in the detachable base. It wasn't enough that it would move during the cut, but the pressure used for putting in a new splinter guard, for example, was enough to move it, which would then result in it going out of square since the blade was being fed into the splinter guard at a slight angle.
So I took it over to the dealer and he sent it out for repair. A week and a half later it came back and is now working perfectly without any further alignment issues. Not sure if this might be your problem, but you could test the base to see.