Sum of dice with negative values only works when the result is positive#917

I created custom dice for the FATE Core RPG system. This system uses special d6 where two sides have a + symbol (value +1), two sides are empty (value 0) and two sides have a - symbol (value -1)

I can give the dice the correct values but when I mark multiple dice (you always roll 4 of them) to see the result, it only calculates the sum, when the sum of the dice values is positive.

So if I have a +1, -1, -1, -1 the result should be -2, but it doesnt add the values up. If the result is positive, like with the values +1, +1, -1, 0 it correctly shows the sum of 1

Is there a way to make it possible, that a group of dice can have a negative sum?