Untextured blocks were created when the id's of certain blocks were changed, therefore they became without a texture. Mushroom blocks, old leaves, old wood blocks etc became untextured. They are semi-rare. A lot of those blocks exist, probably whole islands of old oak wood blocks would be untextured when broken.
Wow Ty Krissy ps. I just tried typing in part of your ign and pressed [Tab] on my keyboard......I play to much Minecraft XD
Idk what the item id is but if you get that item, it would be untextured, but if you place it down, it'll be a still live (cooking) furnace
Nah actually the block texture updates when placed or mines I'm pretty sure. Maybe that's only when it's placed :b