java.lang.Error: type is not fully defined

This minimized case class:

``` scala
case class W[T](seq: Option[Option[T]] = Option.empty)
```

Stops the compilation with the following exception:

```
Exception in thread "main" java.lang.Error: internal error: type of right-hand side Option[A] is not fully defined, pos = <58..98>
```

([full stack trace](https://gist.github.com/OlivierBlanvillain/7594cd2d17f4f6dde879cdb0770c81d1))
