That's a bug for sure.
We lodged a ticket, and fixed it. The updated jar should appear on Sonatype within the hour.
Testing it with the new jar in the REPL, all is now good:
scala> :paste
// Entering paste mode (ctrl-D to finish)
import scala.pickling._
import json._
object JsonTest extends App {
val simplePickle = new Simple(new SimpleProp("TestProp")).pickle
val simpleUnpickle = simplePickle.unpickle[Simple]
}
abstract class SimpleAbstract(val stringWrapper: SimpleProp) {}
class Simple(stringWrapper: SimpleProp) extends SimpleAbstract(stringWrapper) {}
case class SimpleProp(prop: String) {}
// Exiting paste mode, now interpreting.
import scala.pickling._
import json._
defined module JsonTest
defined class SimpleAbstract
defined class Simple
defined class SimpleProp