lambdas and function literals in classes

[John Colvin]

JS asked about this in the main group, but here is more 
appropriate and I'm quite interested myself.

Can someone explain the rationale behind this:
class A
{
    auto a = (){};              //Lambda not allowed
    auto b = function(){};      //Function allowed
    auto c = delegate(){};      //Delegate not allowed
}

A guess:

Delegate's aren't allowed as members due their context pointer 
(why???), lambdas are assumed to be delegates unless they are 
proved to not need context (and dmd is sucking at proving that).