Snape's Predicament

[Arthur Weasley]

No: HPFGUIDX 1231

I thought I posted this a week ago, but somehow it never made it.

Anyway, I was reading book one again and thought about Professor 
Snape.  Quirrell ( who has Voldemort in back of his head) tells Harry 
that Snape was preventing him from finding the Sorcerer's Stone and 
knocking Harry off the broomstick in the Quidditch match.  Since 
Voldemort hears this conversation between Quirrell and Harry, he must 
know that Snape is no longer a loyal Death Eater.  How on earth is 
Snape supposed to be an undercover spy in Voldemort's camp if 
Voldemort already knows about this?  Snape was not present for this 
conversation in book one and may not know anything about it.  Snape 
appears to be in one heck of a predicament.

My other thought on the matter is that Snape has polyjuice potion in 
his office, so he must be able to become other people quite easily if 
he needs to.  Perhaps this is part of his prior service to Dumbledore.

P.S. I think Ludo Bagman will turn out to be a bad guy in the end.