That’s definitely the way it works. See other discussion here where it tripped me up. I would personally prefer it not do this for formats with transparency, or at least have a checkbox somewhere to toggle it.
I think in this case he was talking about “% gray” in the image, not % power in the GFUI. But in a similar way, that’s not entirely accurate, if we’re being picky (and what’s more fun than being picky?) “1%” is too coarse of a measure. There are lighter shades than 1%: even at 8 bits per pixel, there are 256 levels, so a single percent is going to cover 2-3 steps. In any event, what the Glowforge ignores is pure white (in my example, 255). If you’re using the min power setting and don’t want there to be “bald spots” between white (laser off) and almost-white (laser on at min power), you should remap your image to avoid any pure white. @takitus shows an easy way to do that in Vary power glitch (+ workaround) - #14 by takitus.