Or it may be resistance effect wich is currently applying to BASE, and bonus, rounded down, like rolling 1 + 3 => resistance (1/2) + (3/2) => rounded down to 0.5 (=0) + (1.5=1) => 1, something like that.
But yes there are some weird bahavior in calculations sometimes. It will be fixed eventually.
Under the circumstances this seems to be a real possibility. It may just be a badly implemented formula.
