Got a bit of a strange bug; while fighting a Rodian Master of Doomguards, when Master of Doomguards reduced damage from an attack triggered by Sabotage to 0, it appears to have the source -5555.
The floating damage text showed
0
-5555
on two separate lines. This happened every time when they cast Sabotage and the attack was reduced to 0, but never when I initiated an attack, even if it was avoided by Master of Doomguards.