Yep, that's the failure mode. There is an interlock (a notch, actually) that has to be positioned properly to allow the shutter to be depressed. With no film tension, that notch can go into the right place, and enable the shutter release. But with the back-tension from film, that notch may be pulled, and not clear the shutter release.
It can mean that the geared wind head has been installed with the wrong gear alignment.
I've done it myself - on an M2, and the M4 would be similar.