This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 112e. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.
The current wording of _N4868_.220.127.116.11 [namespace.memdef] and 13.9.4 [temp.expl.spec] requires that an explicit specialization be declared either in the same namespace as the template or in an enclosing namespace. It would be convenient to relax that requirement and allow the specialization to be declared in a non-enclosing namespace to which one or more if the template arguments belongs.
Additional note, April, 2015:
See EWG issue 48.
This is a feature request, not a defect.