>>Found an even weirder example. Lyrics of the last song on Uriah Heep's album "Demons and wizards" - "The spell":
>>
>>What do you think I am
>>Do you think I'm dreaming
>>
>>Now what is the meaning of "what" in this case? Surely it's not a request for identification.
>
>You're looking to rock music for grammatical merit?

Sure. Are you saying that these guys invented it by themselves? I'm not giving them that much credit :).

I'm rather convinced they lifted it from somewhere, therefore I'm assuming such usage existed before and elsewhere. This is just where I've found a copy of it.