Cannot initialize unordered_map from int

I've got a really strange problem. MSVC doesn't have initializer lists, so I've used a lambda to approximate them.

static const std::unordered_map<std::wstring, LexedFile::Token> reserved_words = 
    []() -> std::unordered_开发者_高级运维map<std::wstring, LexedFile::Token> {
    std::unordered_map<std::wstring, LexedFile::Token> retval;
    // Do stuff with retval
    return retval;
}();

MSVC throws a compiler error.

error C2440: 'initializing' : cannot convert from 'int' to 
'std::tr1::unordered_map<_Kty,_Ty>'

Unless I'm quite blind, there's no "int" anywhere near this. I don't see what's wrong. Any suggestions?

Edit:

There's nothing funky about // Do stuff with retval, it's just a bunch of insertions, and this is a function-scope static variable in a lambda in a member function.

auto next = [&] {
    static const std::unordered_map<std::wstring, LexedFile::Token> reserved_words = 
    []() -> std::unordered_map<std::wstring, LexedFile::Token> {
        std::unordered_map<std::wstring, LexedFile::Token> retval;
        retval[L"namespace"] = LexedFile::Token::Namespace;
        retval[L"for"] = LexedFile::Token::For;
        retval[L"while"] = LexedFile::Token::While;
        retval[L"do"] = LexedFile::Token::Do;
        retval[L"switch"] = LexedFile::Token::Switch;
        retval[L"case"] = LexedFile::Token::Case;
        retval[L"default"] = LexedFile::Token::Default;
        retval[L"try"] = LexedFile::Token::Try;
        retval[L"catch"] = LexedFile::Token::Catch;
        retval[L"auto"] = LexedFile::Token::Auto;
        retval[L"type"] = LexedFile::Token::Type;
        retval[L"break"] = LexedFile::Token::Break;
        retval[L"continue"] = LexedFile::Token::Continue;
        retval[L"return"] = LexedFile::Token::Return;
        retval[L"static"] = LexedFile::Token::Static;
        retval[L"sizeof"] = LexedFile::Token::Sizeof;
        retval[L"decltype"] = LexedFile::Token::Decltype;
        retval[L"if"] = LexedFile::Token::If;
        retval[L"else"] = LexedFile::Token::Else;
        return retval;
    }();
    if (stack.empty())
        return;
    std::wstring token(stack.begin(), stack.end());
    stack.clear();
    if (reserved_words.find(token) != reserved_words.end()) {
        l.tokens.push_back(reserved_words.find(token)->second);
        return;
    }
    l.tokens.push_back(LexedFile::Identifier);
};

The compiler will accept it if I use the constructor directly not initialization, which seems very strange. Probably a compiler bug.

Calling the constructor with () instead of using = works just fine, so I'm marking this one as a compiler error.