Simply disconnecting 12 volts from the ACC line is not enough to fully turn off the DSATX. It has a microcontroller that is always running even when the computer is off.
Sometimes people experience problems with the Serial port adapter causing weird behavior. This is because when you plug it in when VIN is hot, it can cause a hiccup in the microcontroller.
To reset the DSATX you can either pull the fuse and put it back in, or short pins A2 and B2 with a pair of tweezers or a Key. Make sure you don't short the other pins as you may damage something.