Can't understand how laser mode is supposed to work (1 reply)

Hello.
I converted ender 3 to control my diy laser module, it uses XYENABLE pin to control it with pwm. Original X and Y steppers enable have been pulled down to ground with 100k resistor so it works now.
The problem I'm having is marlin doesn't understand the gcode sent from lasergrbl. I got it to the point where I can do "G1 X10 Y10 F1000 S100" and it will move correctly. I can then do "X5 Y5" and it will still move (remembers G1 code) so that's good. The issue is as follows
Expected behavior - marlin gets G1 move command with S parameter, moves with laser ON, receives next move command WITHOUT S PARAMETER (e.g X5 Y5) so it continues to move to new location with the S power still the same as with the last move, since it was never changed.
Observed behavior - marlin gets first move command with S parameter, goes there with laser ON, on conpletion of said move command it turns the laser OFF and all the next moves are WITHOUT the laser. It seems that moves without S parameter turn the S power to zero.
I want it to not change S parameter if it wasn't specifically told to do so.
Can anyone help with this?