Form 8959 line 24 equals the amount we have already paid in extra Medicare Tax. Line 18 calculated the extra .9% owed. Why is line 24 treating this as extra tax owed?

[tk2010]

Line 22 math equation is the inverse of what it should be.  Line 19 should be subtracted from line 21 which would be a negative number if already paid in what is needed. Form 8959 is missing last calculation of subtracting line 18 from line 22, that answer should go to line 24 in my opinion.