hot-buttered popcorn

At the movies today I was struck by an ad for "hot-buttered popcorn" in the lobby. Hot-buttered popcorn? As in popcorn which has been hot-buttered? While I would never use it, I can see hyphenating two adjectives even when one isn't necessarily describing the second. For instance, if I'm looking at a brick house which has been painted yellow, I would describe it as a "yellow brick house," but I wouldn't necessarily fault someone for writing "yellow-brick house" even though to me that would be a house composed of bricks which are yellow, not just a brick house which has been painted yellow. But when you have two adjectives describing a noun, and the second is a past participle of a verb, it seems to me very odd to hyphenate them in this way. What is it to "hot-butter" something? How would you diagram a sentence like that? Would you have an adjective phrase simultaneously containing two adjectives? It would seem exceedlingly strange to treat "hot-buttered" as a single adjective, yet that seems to be the only thing the authors intended in hyphenating it, unless (perhaps more likely) they simply don't understand what hyphenating two words means. I'm guessing this is what happened, and that thus the phrase "hot-buttered" is completely meaningless, that the authors really intended "hot, buttered" and are unaware of certain conventions of punctuation.