I haven't had this problem previously. I don't know if it's circumstantial at the time I upgraded to 4.0.1 or if it's something different in 4.0.1.
If I leave the computer for a while and the monitor turns off, S3D stops sending print commands to the printer. The commands are send in slow increments with long pauses in between (and the print suffers dramatically) until I go press a key on the keyboard or something to wake the computer back up.
Before I could leave the computer and it seemed like S3D simply grabbed a sleep lock and guarded against this.