Re: Valid C++?

Is this a valid C++ program (according to the C++ standard)? I ask as
I'm trying to port a Windows library to Solaris, and the Solaris C++
compiler reports an error (The name x is ambiguous in ns1: ns2::x and
ns1::x). The code below reproduces the problem, and I wonder now if I
have to adapt the code or submit a bug report to Sun?

namespace ns1 {
  struct x { };
}

namespace ns2 {
  using namespace ns1; // If this line is removed ...
  void x(); // ... or this line the code compiles.
  struct x { };
}

int main()
{
  struct ns2::x x;
}