The MagickWand interface is a new high-level C API interface to ImageMagick core methods. We discourage the use of the core methods and encourage the use of this API instead. Post MagickWand questions, bug reports, and suggestions to this forum.
I have exactly the same problem.
Of course if I declare the -resolution param then IM respects it, but my application manages 500.000 images and each one might has a different resolution.
Does anybody know how to make IM converts keeping the original resolution?