No, the F key works just like it did before, only toggling the ASAS while the key is held, as opposed to the T key which toggles it when it is pressed. The problems is that the ASAS is barely using any force. If you watch your pitch, yaw and roll indicators with ASAS on, you'll see they hardly ever move. They do move ever so slightly. If you have a rocket that can fly steady while only using a very small percent of your available force, be it RCS, Gimbals, torque etc. etc, then you wont have any issues. However, if your rocket/plane needs more than a few percent of your available force then you will drift and be unable to hold a heading. This isn't a case of needing more control surfaces, reaction wheels, rcs thrusters or anything like that. It's that the ASAS will not use those things to their fullest capacity.