Why does the generic case not compile

Question
1

Every now an then i cannot understand the type logic of Scala 3. Suppose i have (simplified as much as i could from my lib):

trait Actor :
  type Accept <: Actor

object Actor :
  type Parent[B <: Boolean] = Actor with Child[B]

trait Child[B <: Boolean] :
  type ChildAccept <: Actor
  type ChildActor <: Actor = B match
    case true  => Actor { type Accept >: ChildAccept }
    case false => Actor
  def reject(child: ChildActor): Unit = ()

trait Select[B <: Boolean, LParent <: Actor.Parent[B]] :
  self: Actor =>
  type Parent <: Actor.Parent[B] = B match
     case true   => LParent { type ChildAccept <: self.Accept }
     case false  => LParent
  def parent: Parent

Now i can define two situations which compile just fine:

trait Leaf_True[Parent <: Actor.Parent[true]] extends Select[true,Parent] :
  self: Actor  =>
  def abandon(): Unit = parent.reject(self)

trait Leaf_False[Parent <: Actor.Parent[false]] extends Select[false,Parent] :
  self: Actor  =>
  def abandon(): Unit = parent.reject(self)

but i cannot define the generic situation:

trait Leaf_Free[B <: Boolean, Parent <: Actor.Parent[B]] extends Select[B,Parent] :
  self: Actor  =>
  def abandon(): Unit = parent.reject(self)

this gives:

[error] 336 |  def abandon(): Unit = parent.reject(self)
[error]     |                                      ^^^^
[error]     |Found:    (Leaf_Free.this : Actor & Leaf_Free[B, Parent])
[error]     |Required: ?1.ChildActor
[error]     |
[error]     |where:    ?1     is an unknown value of type Leaf_Free.this.Parent²
[error]     |          B      is a type in trait Leaf_Free with bounds <: Boolean
[error]     |          Parent is a type in trait Leaf_Free with bounds <: Actor.Parent³[B]

why is that? Every possible type value of B works. Of course, you should not have the two parameters different from each other. Or should you also consider Nothing as a separate subtype? (extending appropriately did not help). Is there a way to overcome this somehow? I would not like to write out every case manually with different traits. Not very DRY.

BTW, i also tested this in 3.3.0-RC6 but this does not make a difference. Thanks for any insights here.