Signed area graph problem

[lrdheat]

I think I have found an oddity when evaluating the function...as we approach zero from above, the function approaches .25 (which the Prime correctly produces when I take the limit). When substituting small numbers into the function, it does approach .25, but smaller than .001, such as .0001, Prime comes up with 0.

Perhaps this is the problem.

I am in standard display as opposed to fix option. Is there some other setting that is producing this behavior?