OK I updated the manual page.
I see what you mean now. For some reason I assumed Panda3d would silently modify the UVs in this mode. But that doesn’t make much sense.
If anyone is curious, that mode shouldn’t affect this function. So if you want to use non power-of-two only for GUI images and load them with a function like this, you shouldn’t have to worry. For every other case if you don’t want to modify your texture scale manually, you can just go with “textures-power-2 up”.