using function overloading with lambdas

["variadic.template" <variadic.template@xxxxxxxxxxxxxx>]

Hi,

I'm playing around with std::function and lambdas with
a snapshot of g++, trunk revision 152966. Compiling
the following code with -std=c++0x results in

test.cpp: In function 'int main()':
test.cpp:17:48: error: call of overloaded 'foo(main()::<lambda()>)' is  
ambiguous
test.cpp:4:6: note: candidates are: void foo(std::function<void(long int)>)
test.cpp:9:6: note:                 void foo(std::function<void()>)

#include <iostream>
#include <functional>

void foo(std::function<void(long)> bar)
{
  bar(5);
}

void foo(std::function<void()> bar)
{
  bar();
}

int main()
{	
  foo(std::function<void()>([](){std::cout << "foobar" << std::endl;}));   
// OK
  foo([](){std::cout << "foobar" << std::endl;});                          
// Line 17: Error
}

Is it a bug or the behaviour as the standard suggests? In theory, gcc  
should be able
to deduce the right type by the parameter-list of the lambda - or am i  
missing
something?