Unexpected behaviour with match statements

[jcp19]

The following code snippet is accepted, even though it should be rejected:

type list adt {
	Empty{}

	Cons{
		head any
		tail list
	}
}

ghost
decreases l
func length(l list) int {
	match l {
		case Empty{}:
			assert false // <--- assert false here should be reachable
			return 0
		default: 
			return 0
	}
}