When multiple resource packs, each with an iron ore texture, are used simultaneously, iron ore blocks will display textures from both (see attached image, top part).

Also, when mining an iron ore block, the mining particles coming off are the standard "texture not found" magenta and black squares. (I know I'm supposed to add separate bugs as separate issues, but I thought these are probably symptoms of the same bug. Sorry if I'm wrong.) (See attached image, bottom part.)