Template function causes a compiler error when used with local lambda

My previous question concluded that a distasteful "double cast" might be necessary to use the POSIX makecontext with a C++ lambda function (i.e. function object). Moving on, I'm now faced with a compilation error relating to the following minimal code:

#include <iostream>
#include <ucontext.h>

using namespace std;

template <typename T> void foo()   {
  ucontext_t c;
  auto f = [=](int i){ cout << i << endl; };
  makecontext(&c, (void (*) (void)) (void (*)(int)) f, 1, 12345);
}

int main(int argc, char *argv[]) {
  foo<int>();
  return 0;
}

The error is:

error: invalid cast from type ‘foo() [with T = int]::<lambda(int)>’ to type ‘void (*)(int)’

However, if I remove the unused (in this example) template argument from the foo function, so it becomes void foo();, and change the call to foo() the error disappears. Could someone tell me why? I'm using G++ 4.6.

Edit:

From the comments below, it seems the [=] in the code above causes the lambda to be a "capturing" lambda, regardless of the fact that it doesn't actually capture anything. The [=] is not necessary in my code, alas replacing with [] in GCC 4.6 does not remove the error. I am installing GCC 4.6.1 now...