My dog digs no matter what, as with Lala's Shih tzu she also tries to dig inside. For her I think its a natural reaction.
Doesnt matter how tired she is or whether shes with other dogs, its not excessive just in a few particular places.
I agree with the fact that dogs are dogs, as long as its not destructive because they are bored its fine.. They dont understand that the annoying little grass bits are actually beautiful flowers... sigh