Noticed on Musketeer 1.0.4 - when hammering stone into a variant and then mining it, it drops stone instead of cobblestone. One could see it as a QOL feature, but since it's inconsistent with the full block I would assume it's unintended behavior.

so this is part of how variant selector works. That config is off by default and when turned on care must be taken, fixing related recipes to avoid dupes. You could consider it either a bug of the modpack or a feature of it. You can turn that feature off altogether in the config