[boost] [Signals] Call of an unary object function from a binary signal does not fail to compile

Hello, Almost everything is in the title. To go into details, I have a small test case (see attached file) where I accidentally manage to call a unary object function from a binary signal. The object function is the result of a Boost.Bind call. I would have expect a compile time error here. What happend to the second parameter ? Is there any risks of stack corruption ? Thanks, Samuel