Just curious about this behavior.  After looking at all the very nice bunny condos here at binkybunny, we decided to build a condo for our two bunnies.  The bunny condo has been in their pens for about 2 weeks.  

The floor of the condo is a piece of wood covered with some padding and fleece fabric.  The bunnies each dig at the fabric and pull at the fabric.  Its pretty aggressive.  If I go to pet them, they settle.  Both bunnies are male and neutered. Their living area is carpeted but they do not dig. 

Again, curious about the digging behavior.  I haven't seen it before. 

Digging is natural to rabbits, it is a form of play and a natural instinct. Fleece lining is a favorite of my two as well, they have a cat hideaway/scratching post toy and it has (had) a fleece lining to the inside ... well, it's about 90% destroyed from digging, but it's fun to them, so I will probably end up buying some cheap fleece to reline it.

Ditto, it's very natural. My bunnies will dig blankets or towels. They dig them and bunch them all up. Sometimes biting the fabric will happen with the digging so make sure they are not biting and ingesting any fabric.

I have a couple of buns who like to dig alot and a couple that don't. I would say its more the personality of the rabbit.