This bug is fixed in git (commit 727fe82).

First reported at https://groups.google.com/forum/#!topic/sage-support/qexNzA3iDzE

See downstream report at http://trac.sagemath.org/ticket/16176

(%i1) load(simplify_sum); (%i9) simplify_sum(sum(1/x^2,x,2,inf)); 2 %pi (%o9) ---- - 1 6 (%i10) sum(log(1-1/x^2),x,2,inf); inf ==== \ 1 (%o10) > log(1 - --) / 2 ==== x x = 2 (%i11) simplify_sum(sum(log(1-1/x^2),x,2,inf)); inf + 2 (%o11) log(-----------) 2 (inf + 1)