Assignment fails for union structure field

[pabuhr]

forall( dtype T )
union Link {
	struct {
		T * top;
		uintptr_t count;
	};
	__int128 atom; // both fields
};

int fred() {
	Link(int) l;
	int i = l.count, * ip = l.top;
	__int128 I = l.atom;
	i = l.count;
	ip = l.top;
	I = l.atom;
}

CFA Version 1.0.0 (debug)
test1.cfa:15:1 error: No reasonable alternatives for expression Applying untyped:
  Name: ?=?
...to:
  Name: ip
  Untyped Member Expression, with field: 
    Name: top  ... from aggregate:
    Name: l

The assignment fails because top is of type T. Assignment to non-polymorphic types works.