I have an extensive background in linguistics and taught it before At no time was there ever a compound in English in which they were two words Compounds are single words not phrases The whole concept of compounding is merging two words together as one By definition a compound is a lexeme and lexemes do not have spaces in the middle of them An item with a space is a phrase  As I proved above it does not  Many sources say otherwise There was a whole section devoted to listed references Look under Scope and you can see where it lists references provided