Post any defects you find in the released or beta versions of the ImageMagick software here. Include the ImageMagick version, OS, and any command-line required to reproduce the problem. Got a patch for a bug? Post it here.
What difference should it make for me how the resolution is stored internally? (In pixels per meter, by the way.) Imagemagick is capable of converting between resolution units, so it shouldn't matter.
Anyway, the implementation disagrees with the documentation, which means one of them has a bug. It's your choice which one.