Quoted From Borderlands Wiki
When the total is negative, borderlands uses another formula. Instead of directly applying the modifier, Borderlands applies it to a reciprocal function. For example, for a gun with a spread modifier of -130% from a barrel5, the modifier will be of 1/(1 + 1.3); if that gun had a base spread of 2, the final spread would be 0.87.
The rationale for this mechanic is to have the same scale of effect, regardless of the modifier's sign.
A notable list of stats that are affected by this rule are:
-Damage: Many weapon parts actually have negative bonuses.
-Spread: Very often breaks the -100% bar.
-Damage reduction: Brick's Juggernaut skill; Lilith's Silent Resolve and Resilience skills; Roland's Grit skill.
-50% Damage Reduction => Player takes 66% Damage
-100% Damage => Player takes 50% Damage
-Recoil: Internally, the game uses a "Recoil" stat, which it displays as its inverse, "Recoil Reduction"
So I think it will be same for borderlands 2 :)