C++ Compiler Deducing Incorrect Template Parameter

I'm trying to figure out why the following fails to compile when I pass in the variable "a" as an lvalue to attach(), but compiles fine when I pass it in an rvalue, e.g. with std::move().

#include <cstdlib>

class Test
{
public:
    Test() {}
    ~Test() {}

    bool func(char c)
    {
        return true;
    }
};

template <typename R, typename C, typename T1, typename... T2>
bool attach(C& obj,
            R(C::*func)(T1,T2...), T1&& arg1, T2&&... args)
{
    return true;
}

int main(int argc, char** argv)
{
    Test test;
    char a = 'a';
    attach<bool,Test,char>(test, &Test::func, a);

    return EXIT_SUCCESS;
}

Here, why isn't "a" deduced as an lvalue according to the template collapsing rules?