+ operator with reference parameters can not be chained

[Mircode]

Hi!

this doesn't compile:

class myclass{};

myclass operator+(myclass &a, myclass &b){
	return a;
}

myclass a,b,c,d;
d = a+b+c;

when I change

d = a+b+c;

into

d = a+b;

then it compiles and if I change

operator+(myclass &a, myclass &b)

into

operator+(myclass a, myclass &b)

it also compiles.

What is the problem here?

Best regards,
Mirko

[MiiNiPaa]

myclass operator+(const myclass &a, const myclass &b){