Here is the answer from Wolfram support I received today:

When Mathematica returns the input as the output, it means that the calculation returned unevaluated. This often means that the function does not have the methods available to solve the problem symbolically, or it is mathematically impossible to obtain a symbolic solution (not all sums, integrals, or differential equations have symbolic solutions after all). It appears that in earlier versions Mathematica was incorrectly returning 0. The developers have since corrected that incorrect result. Now it more appropriately returns unevaluated since it is not able to find a symbolic solution for that sum.

The sum cannot be resolved and there should not have been a dependancy on a redundant parameter.