v1.10beta 100+ immunities acting as psuedo absorb:

[Crystalion]

In another test I set up a monster to do 50 physical, 50 lightning, and 50 fire damage.

-With 60 MDR, the total damage comes out to be 30 (while it should be 50).
-With 60 MDR and 50 physical resistance, the total damage comes out to be 5 (when again it should be 50).
-With 90 MDR, the total damage becomes 0.
-With 60 DR, the total damage becomes 90.
-With 60 DR and 50 phys resist, the total damage is still 90.
-With 120 DR, the total damage becomes 30.
-With 150 DR, the total damage becomes 0.

The theory so far is that when MDR/DR makes the amount of damage for a given type negative, that negative value doesn't get corrected to 0. When they're negative, resistance and absorb steps would get skipped over and that negative amount ends up reducing the total amount of damage done when all the final damage amounts for each type get summed together way at the end of the damage modification process.

Lovely work.

Could you check an attack that does have physical and one that doesn't have any type of non-physical (as control tests, to ascertain, e.g., whether >0 damage must be present for the MDR or DR to have any effect)?

Could you check an elemental (or, iirc, Crescent Moon "magic") direct (not percent) absorb as well (looking for the negative underflow summation effect, naturally)?