Casting an object with events defined to an interface type causes an internal compiler error

I've got an interface with a simple signature:

namespace Serial {

public interface struct ISerial
{
    uint16_t func1();
    uint16_t func2();
};
}

and then a class type which implements the interface

namespace Serial {
    public delegate void MyEventClass();

public ref class MySerial sealed : public ISerial {
public:
    event MyEventClass MyEvent;

    MySerial();

    ...
};
}

but elsewhere, as a default parameter to a function, I try to store a reference to a type MySerial as an ISerial ^

void
begin(
    Serial::ISerial ^s = ref new Serial::MySerial
);

causes: error C1001: An internal error has occurred in the compiler.

when I remove the event from the class definition, everything compiles fine. I'm finding little information on this error.