This isn't just some subtle implementation detail; the aliasing noise is obvious and IMO it's an important part of the sound. I personally like it, because it adds some extra high frequency content that would otherwise be lacking in many Amiga modules because of low quality samples. libopenmpt supports Amiga-style resampling with the render.resampler.emulate_amiga option. Although it's not documented in the man page, you can enable it in openmpt123:
