__interface keyword not practicable when derived class exports to dll?

[FriendOfAsherah]

I found out that

__interface I { };

class __declspc(dllexport) C: public I
{
}

does not work because C then needs the assigment operator I::operator =() when compiler generates default implementation of C::operator =(const C&) I can overcome this implmenting a C::operator= but whats the reason of implementing operator = for dllexport? any other way to solve this?