It's distributing across all positions, as it should. If it were inconsistent in this regard, that would be a (serious) bug.
I believe a common approach to this is to use a replacement rule. I am not on a machine with Mathematica at the moment, but something like the following.
x*y*Inactive[Sum][1/n^2,{n,1,Infinity}] /. a_. * Inactive[Sum][b_,c__] :> Inactive[Sum][a*b,c]
