Sounds like my dog. She only does it with some treats and real bones (raw from the butcher). Since it's only with "special" treats, I think she's saving it for later and wants it all to herself. I'm sure they had to store food in secret in the wild.

Also I know for a fact that she goes back and digs up her stash. She had a bone at our vacation house that she would relocate each time we visited there - as soon as she jumped out of the car. One time a neighbor dog sniffed around where she hid her bone (I watch her bury them, she's not skilled at the secret thing) and she FREAKED OUT on the dog, unusual for my normally submissive wimp.