Hoag and virulance bug with damage reduction

If you use lancing steel of spraying with level 2 chance to poison support(tooltip 46-188 physical damage, 14-11 chaos damage, attack time 0.46) to apply poison in for example incarnation fight then you max out at 25 virulance but if you change to level 19 chance to poison gem(tooltip 46-188 physical damage, 287-428 chaos damage) then instantly get 90 virulance.
For some reason damage reduction rounds the damage down to 0 so you cant apply poisons.
Same thing happens with delirium damage reduction if you stack the effect from mirror and go fight the boss other side of the straight line- far from mirror.