Error message uses "Concrete type" to refer to an interface

[tombentley]

interface A of X | Y {}
interface X satisfies A {}
interface Y satisfies A {}
interface Z satisfies X&Y {}

error: concrete type is a subtype of multiple cases of enumerated supertype 'A': 'Z' inherits 'X' and 'Y' [ceylon-compile] interface Z satisfies X&Y {} [ceylon-compile] ^

I always understood that a "concrete type" was any type that was not abstract, and that interfaces are abstract, so I find the error message confusing. I don't see why the type's concreteness is relevant to the error.

[gavinking]

Fixed, thanks.