No, that's simply a numbers bug, and how it's coded. When a creature burrows, it's attack power gets halfed. And when it unburrows, the attack power gets doubled. Zanz has it coded to round down when you burrow, so burried a 9/4 becomes a 4.5/4, rounds down to a 4/4. Then when it doubles, it goes back to 8, because that's 4*2.
Or at least, that's how I think that's how it works.
