Why does one hermit crab 'stand guard' while the other is molting under the sand?

One of my hermit , in the main tank, decided to begin it's molting process and buried itself under the sand under some driftwood. One of the other has sat next to it under a little ledge the entire time and will not move from this spot. He has dug a little bit of a hole in the sand but nothing major. He still continues to go out and eat once in a while but has otherwise become very lethargic. Is this normal behavior or is he waiting to snatch up the new crab for food once it emerges? (I've read they do this if not separated)