FWIW, I haven't noticed any problem with upvoting.
I've seen it with both, but not sure I saw the same thing you did.
In any case, a possible divide by zero error depending on the numbers? I don't recall what the formula is, but if there's a ...
A/(B-C), if B-C=0, that would throw an error, or else B-C can go negative, making the total number of possible upvotes be negative? Just stabbing in the dark, since I don't know the exact formula.