Brahmin/Gecko hides

[Sir Craftkid]

There seem to be some places(namely almost everywhere other than encounters) where the above mentioned animals do not drop skins
Brahmins: So far I have only found that the one in vault city spawn does not drop skins
Geckos: All mines that have them, and I once had a gecko drop in to rt encounter that didn't drop skin

[Kilgore]

Only brahmins and geckos in encounters drop skins. Not a bug.