For what it's worth, here is how I understand this.
In 07/08, Howard took 4 3pts attempt out of 974 shots. That's 0.4 % which belongs to perimeter shooting. If you round this to the closest integer number, it's still 0%.
I don't have the stats (nor do I know how WIS calculates them) for mid-range and paint but, if it's something like 10.3% and 89.3% respectively for example, the sum of the 3 area equals 100% (0.4 + 10.3 + 89.3) but the sum of the rounded values only equals 99 (0 + 10 + 89).
I don't think displaying (0.4, 10.3, 89.3) or (0, 10, 89) changes much the outlook of Howard's offense and this difference wouldn't influence my choice when setting my defensive strategy against that player. From what I understand, this is the only thing these numbers are used for anyway.
So I think it's just a round off issue and it's probably not even a mistake to begin with. I admit it might be misleading or confusing at first sight though.