If nothing else is working, you could resort to constructing the formula in a more tedious way where you print it piece by piece instead of using one single MathObject formula. Since you know you are dealing with:
y = ±m x ± b
where m may or may not be a fraction, may or may not be 1, it wouldn't be too hard to do that. It would make the problem code less easy to read, and might take significant time if you have many problem files like this.