Type mismatch when `unapply` returns a type parameterized with a singleton type

[noresttherein]

Reproduction steps

Scala version: 2.13.16

	trait Contains[-C, -X] {
		def apply(items :C, item :X) :Boolean
	}
	object SetLike {
		def unapply[X](items :IterableOnce[X]) :Option[Contains[items.type, X]] =
			items match {
				case set :collection.Set[X @unchecked] => Some(
					(new Contains[collection.Set[X], X] {
						override def apply(items :collection.Set[X], item :X) :Boolean = items(item)
					}).asInstanceOf[Contains[items.type, X]]
				)
				case _ => None
			}
	}

	def contains[X](items :IterableOnce[X], item :X) :Boolean = items match {
		case SetLike(contains) => contains(items, item)
		case _ => SetLike.unapply(items) match {
			case Some(contains) => contains(items, item)
			case _              => items.iterator.contains(item)
		}
	}

Problem

type mismatch;
 found   : items.type (with underlying type IterableOnce[X])
 required: <unapply-selector>.type
		case SetLike(contains) => contains(items, item)

Calling unapply directly and then matching a value already parameterized with a singleton type, as in the second case in contains works as intended.