Marlin responding differently to pronterface commands vs SD card gcode

Been testing my ATMega256 marlin laser engraver with pronterface, and all the motion commands work, and things like G0 S200 X60 Y60 will move the head and also activate the laser for the entire motion. Great. I put the same in a gcode test file to run from an sd card:
G1 S200 X100
G0 S200 X100 Y60.333
G1 S200 X0
G0 S200 X0 Y60.667
G1 S200 X100

a simple back and forth scanning pattern ... and the laser blinks every time the command changes - that is, when it changes direction, I see the laser flash briefly - but for the rest of the time the laser is off. Why might this be?

Not sure if this is related, but I can also manually turn the laser on with M4, but then any motion immedialtey turns it off again.

Appreciate any advice or things to try! Can also provide more detail and context if needed, apologies if this was not enough.

... mybe you have to insert the Y-value too, even if it doesn't change?

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

It almost sounds like the laser command is inverted? The laser is off when it should be on, and on when it should be off?

Ok so this is frustrating for anyone looking for answers but I tried it today and it ... just worked. No idea why. Sorry all who have the same problem, but thanks those for suggestions?

... good, it works!

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Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]