https://issues.dlang.org/show_bug.cgi?id=21345

          Issue ID: 21345
           Summary: [C++,posix] different mangling between string and
                    non-string namespace in "std"
           Product: D
           Version: D2
          Hardware: x86
                OS: Mac OS X
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: dmd
          Assignee: nobody@puremagic.com
          Reporter: iamthewilsonator@hotmail.com

version(UseString)
{
    extern(C++, `std`) void a(){}
    pragma(msg, a.mangleof);// _ZSt1av
}
else
{
    extern(C++, std) void a(){}
    pragma(msg, a.mangleof);// _ZNSt1bEv
}

Not sure which one is the correct one, but they should both be the same.

--