I propose adding a scaling amount of blunt damage on bullet deflection, amount of which would be dependent on weapon damage deflected.
x0.3 or x0.2 of damage transferred as blunt impact trauma, possibly to multiple locally-related areas.
The reason for this is simple. You can't magically deflect all of the energy the bullet is carrying, some of it will be transferred into the object it collides with.
I actually wrote a design for this a few days ago on the "balancing process" thread in General, Piotr's implementing it now.
Good job, I can already see it working in the game ;D