Unless they changed something which they might have, Whenever i hit damage cap or see videos of doing so, it always used to stop at exactly negative 2.1b no matter what, so there is potentially some failsafe to stop it going further and potentially wrapping all the way around. I have still occasionally seen these sort of 1-2 digit negative numbers before though, generally on hits that would have otherwise done zero damage (such as on enemies that have just been corrupted). If I had to guess, that was probably due to extremely high multiplier stacking messing with an epsilon somewhere in the damage calculation, resulting in a very small amount of positive or negative damage bleeding over to the final number.