Blitzmax makes everything rounded UP to the nearest power of 2, and SQUARE.
Why would it do that? Blitz3d certainly doesn't.
all my sprites are 53 X 42 and I ain't changin 'em. Dagnabbit!
Fortunately, you don't really need to. I'm not sure whether BMax adjusts the UV coordinates or just scales your sprites, but it takes things into account either way. It would be much better if it adjusted the UV coordinates though, because resizing makes them unecessarily blurry. You're effectively scaling up and then scaling back down again when you draw. Which would be silly.