i get fv = 25*(1.15^40-1)/(1.15^(1/26)-1) = 1,237,786.9304496213
The answer listed in the PPC Journal. You're quite right.
I note that the calculators with greater precision (19BII, 48GX, etc) give the answer similar to the one you show.
The 12c and 12c platinum really should give the same answers, especially if they are sold as "compatible".