(sorry for the long explanation)
No, but I now know what is going on.
In T2Laser the footer at the end of my G-Code generator sends:
M03 S0 (laser power 0)
M05 (laser disable)
Then, it moves back to the origin:
G00 X0 Y0 Fx
It is this move that causes the PWM to re-enable (must be something with the firmware, how they implemented the spindle control to allow changes on-the-fly)
If I end the program with an M2 or M30 this PWM signal stops but that also has a side effect of resetting Grbl and losing the home position, something I would prefer not to do (perhaps I could make this optional). This has been fixed by chamnit (Sonny Jeon) the current developer of Grbl in later versions of the master.
So back to your question, since the test G-Code I used for the laser power ramp up/down didn't have any moves after the laser power settings it did correctly shut off all PWM signal.