[c++0x] pair's variadic constructor (N2369, 20.2.3.4)

[CoffeeBuzz <chris dot fairles at gmail dot com>]

template<typename _U1,  typename... _Args> 
pair(_U1 && __x, _Args &&... __args)
: first(std::forward<_U1>(__x)), second(std::forward<_Args>(__args)...) {}

I can't seem to find information as to why this was added to the standard.
It seems to me that its just some syntatic sugar to initializing pairs. For
example:
pair<int, pair<double, string>> p(1, 2.3, "Hi mom."); 
struct A { A(int, int) {} }; 
pair<int, A> p(1,2,3);

However, after implementing the full spec, I get some odd deduction behavior
in all the ctor overloads. Take the following mock-pair class:

template <typename T1, typename T2>
struct P {
    P(){}
    P(P && p) {}
    P(T1 const& t1, T2 const& t2){}

    template <typename U1, typename U2>
    P(P<U1,U2> const& p) {}

    template <typename U1, typename U2>
    P(U1&& u1, U2&& u2) {}

    template <typename U1, typename U2>
    P(P<U1,U2> && p) {}

    template <typename U, typename... Args>
    P(U && u, Args&&... args) {cout << "why?"; }
};

When I compile the following code:
P<int,int> p1(1,2); 
P<int,int> p2(p1);

It seems that the construction of p2 is not done by P(P<U1,U2> const& p)  or
P(P&& p) as I might have expected. Instead, P(U && u, Args&&... args) is
chosen with U being type P<int, int>& and Args is no type (empty pack). 

Now this is an issue because in the pair, this variadic ctor forwards u to
"first" and args to "second" but first is type int, and not P<int,int>& and
thus errors. So, how do you stop this behavior?

Chris
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