Inherited type symbol problem

[LPTK]

See the scastie.
The code is reproduced below:

class Base {
  class A
  class B extends A
  type of[+A0 <: A,T] = A0
}
object Base extends Base
import Base._
object Main {
  def foo = new B
  def foo2: B of Any = foo
  
  def main(args: Array[String]) = ()
}

Fails with:

-- [E056] Type Mismatch Error: /tmp/scastie722928142903515025/src/main/scala/main.scala:10:12 
10 |  def foo2: B of Any = foo
   |            ^
   |       Type argument Base.B does not conform to upper bound Base.this.A 

It works in Scalac, and it works in Dotty if the definitions are moved to the object!

PS: note that it has nothing to do with object Base having the same name as class Base.

[smarter]

Hmm, I guess there's a missing substitution somewhere. Here's a minimization:

class Foo {
  class A

  type Bla[X <: A] = X
}

class Bar extends Foo {
  val y: Bla[A] = ???
    // error: Type argument Bar.this.A does not conform to upper bound Foo.this.A 
}