P.P.S. Minor correction... Substance Painter uses a 0.0-->1.0 scale for Metallic and Roughness and -1.0-->1.0 for Height. With a high degree of precision, such as "0.571429" (literally copied from Substance Painter's value for Roughness) if you want to type in a value.
Speaking of a -100 to +100 scale, I would expect ZERO to be BLACK, so a scale from 0->100 would be more appropriate. Or 0->255 if you have that many levels of gray. P.S. In Substance Painter, the height map goes from -100 to + 100, but that is because it can bump out (positive) or dent in (negative) and 0 (gray) is surface level with no height/depth applied. But they don't do that for Metallic or Roughness.
Oh, I only now have seen, it happens only, when the texture is inverted. So maybe not really a bug, but confusing.