Snape -- yet another clue

[UNIX4EVR]

No: HPFGUIDX 144748

Having just finsihed a re-read of GOF I found yet another nugget.

Earlier I mentioned the 6 people Voldemort said weren't among the DE 
in the graveyard.  3 were dead.  One was a coward (Karkarov), one had 
deserted him (Snape?) and the other and helped get Harry there (Barty 
Crouch Jr.).

Now for clue #2.  Take it for what you will.

When Dumbledore is sending Sirius and Snape off to their tasks he 
sends Snape off and a "look a aprehension crossed his face."

Dumbledore was apprehensive about Snape?  Why????  Did he question his 
loyalty -- or was he worried FOR Snape?