I'd say it's a problem.

You cannot expect your body to respond to intense demands if you're not fueling it. When activity level increases dramatically you need to compensate by increasing fuel to meet that demand - especially if you're taking muscle growth.

I'm not saying the caloric deficit is too low - guys like Lyle MacDonald and Scott Connelly are saying it's too low, i'm just repeating what I've read!

I'd look into finding a good calculator for RMR and learning a little bit about how much fuel I really needed to eat to lose weight.

This is a great place to start:

http://www.weight-loss-i.com/metabolism.htm

Best,
Nat