wifstream with imbue, locale produces valgrind err

I implemented a language detector using ngrams and all works fine so far. In order to detect a bunch of languages I have a set of language dependent ngrams files for each supported language my detector needs to read in before the actual detection is started.

For reading these files I set the systems default locale (which on my ubuntu machine is en_US.UTF-8) like so. These code snippets are in my language_identifier constructor:

std::locale def_lc(""); // --- line 37 (see valgrind)
const utf8_codecvt_t &utf8_codecvt = std::use_facet<utf8_codecvt_t>(def_lc);
std::locale utf8_locale(def_lc, &utf8_codecvt);

I set the locale via imbue before I open the stream:

wifstream is;
is.open(filename.c_str(), ios::in);
is.imbue(utf8_locale);
if (is.is_open()) {
   // ... 
}

Executing my detector, valgrind gives me following output:

==21669== Memcheck, a memory error detector
==21669== Copyright (C) 2002-2011, and GNU GPL'd, by Julian Seward et al.
==21669== Using Valgrind-3.7.0 and LibVEX; rerun with -h for copyright info
==21669== Command: ./language_identifier
==21669== 
==21669== Invalid read of size 8
==21669==    at 0x56E5E08: wcscmp (wcscmp.S:479)
==21669==    by 0x4EA2113: std::moneypunct<wchar_t, false>::~moneypunct() (in /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.16)
==21669==    by 0x4EA2198: std::moneypunct<wchar_t, false>::~moneypunct() (in /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.16)
==21669==    by 0x4E96A79: std::locale::_Impl::~_Impl() (in /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.16)
==21669==    by 0x4E96C4C: std::locale::~locale() (in /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.16)
==21669==    by 0x40429E: language_identifier::language_identifier() (language_identifier.cpp:137)
==21669==    by 0x409802: Singleton<language_identifier>::instance() (Singleton.h:29)
==21669==    by 0x4050C1: main (language_identifier.cpp:270)
==21669==  Address 0x5a07248 is 0 bytes after a block of size 8 alloc'd
==21669==    at 0x4C2AC27: operator new[](unsigned long) (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==21669==    by 0x4EA1DED: std::moneypunct<wchar_t, false>::_M_initialize_moneypunct(__locale_struct*, char const*) (in /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.16)
==21669==    by 0x4E9911E: std::locale::_Impl::_Impl(char const*, unsigned long) (in /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.16)
==21669==    by 0x4E9965E: std::locale::locale(char const*) (in /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.16)
==21669==    by 0x403C36: language_identifier::language_identifier() (language_identifier.cpp:37)
==21669==    by 0x409802: Singleton<language_identifier>::instance() (Singleton.h:29)
==21669==    by 0x4050C1: main (language_identifier.cpp:270)
==21669== 
==21669== Invalid read of size 8
==21669==    at 0x56E5E08: wcscmp (wcscmp.S:479)
==21669==    by 0x4EA2003: std::moneypunct<wchar_t, true>::~moneypunct() (in /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.16)
==21669==    by 0x4EA2088: std::moneypunct<wchar_t, true>::~moneypunct() (in /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.16)
==21669==    by 0x4E96A79: std::locale::_Impl::~_Impl() (in /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.16)
==21669==    by 0x4E96C4C: std::locale::~locale() (in /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.16)
==21669==    by 0x40429E: language_identifier::language_identifier() (language_identifier.cpp:137)
==21669==    by 0x409802: Singleton<language_identifier>::instance() (Singleton.h:29)
==21669==    by 0x4050C1: main (language_identifier.cpp:270)
==21669==  Address 0x5a07478 is 0 bytes after a block of size 8 alloc'd
==21669==    at 0x4C2AC27: operator new[](unsigned long) (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==21669==    by 0x4EA17FD: std::moneypunct<wchar_t, true>::_M_initialize_moneypunct(__locale_struct*, char const*) (in /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.16)
==21669==    by 0x4E9916B: std::locale::_Impl::_Impl(char const*, unsigned long) (in /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.16)
==21669==    by 0x4E9965E: std::locale::locale(char const*) (in /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.16)
==21669==    by 0x403C36: language_identifier::language_identifier() (language_identifier.cpp:37)
==21669==    by 0x409802: Singleton<language_identifier>::instance() (Singleton.h:29)
==21669==    by 0x4050C1: main (language_identifier.cpp:270)
==21669== 

--- lang is en

--- lang is zh

--- lang is de

--- lang is ja

--- lang is ja

--- lang is zh

--- lang is zh

--- T1: lang is de

--- T2: lang is de
==21669== 
==21669== HEAP SUMMARY:
==21669==     in use at exit: 0 bytes in 0 blocks
==21669==   total heap usage: 366,286 allocs, 366,286 frees, 17,016,689 bytes allocated
==21669== 
==21669== All heap blocks were freed -- no leaks are possible
==21669== 
==21669== For counts of detected and suppressed errors, rerun with: -v
==21669== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 2 from 2)

I can not exactly remember and have no chance to check, but on my ubuntu 10.04 LTS machine I had no above valgrind errors, but I may mistaken.

I can also reproduce this with this simple program:

#include <iostream>
#include <locale>

int main (int argc, char **argv) {
    try {
        std::locale * l1 = new std::locale("de_DE.UTF-8");
        delete l1;

        std::locale l2("de_DE.UTF-8");

    } catch(...) {
        return 0;
    }
    return 0;
};

Does anybody know what's going on here? Do I miss something?

Code is built on ubuntu 12.04LTS, using gcc version 4.6.3 (Ubuntu/Linaro 4.6.3-1ubuntu5)

$ /lib/x86_64-linux-gnu/libc.so.6
GNU C Library (Ubuntu EGLIBC 2.15-0ubuntu10.3) stable release version 2.15, by Roland McGrath et al.
Copyright (C) 2012 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.
Compiled by GNU CC version 4.6.3.
Compiled on a Linux 3.2.30 system on 2012-10-05.
Available extensions:
    crypt add-on version 2.1 by Michael Glad and others
    GNU Libidn by Simon Josefsson
    Native POSIX Threads Library by Ulrich Drepper et al
    BIND-8.2.3-T5B
libc ABIs: UNIQUE IFUNC

Thanks for your hints!