Gruntly, I made a double adapter up for the obd plug so my laptop can stay connected to scan tool without car being connected. I have to start with scan tool connected (to the car) because it looks for the module first, but when I send a command, I unplug from car just before. The scantool tells me its not connected, but not before it sends the command.
Maybe your scantool requests module presance each time u command the module?