Storing lambdas as members confusion

I was reading Scott Meyer's Effective Modern C++ and hit the item in which he's suggesting usage of lambdas in place of std::function and std::bind. I understand his argument and his claim about drawbacks of std::function and I agreed with him.

As of today, I decided to switch to templates for storing lambdas (which do not need mutators). I do understand that type of every lambda is only known to the compiler and even two identical lambdas will have different types so how come the following code compiles and works just fine?

template<typename LambdaT>
class CaptureLambda
{
public:
    CaptureLambda(const LambdaT& fn)
        : mActionFn(fn) // initialize mActionFn to a user supplied lambda
    {}

private:
    LambdaT    mActionFn{ []{} }; // initialize mActionFn to an empty lambda
};

My point of confusion is that, how come mActionFn is default initiated to an empty lambda with a different type inside member declarations but the constructor of the class is happily accepting another type of lambda in its arguments? are they castable to each other? if yes, why the following makes the compiler sad?

// Class stuff...

template<typename T>
void resetActionFn(const T& newFn) { // setter member
    mActionFn = newFn;
}

// Class stuff...