I've encountered this off and on over the last few years from Flash CS3 to CS5. It doesn't happen on everything but right now I've got some hair I'm creating and I've spent the last 30 minutes trying to add anchor points and only successfully been able to add 3 or 4. Most of the time, adding an anchor point just makes my entire drawing disappear. Has anyone else encountered this? My work has all but come to a stop because of this problem.