Ammonite PPrint derivation failing

AmmonitePPrintTest.scala

import ammonite.pprint._, Config.Defaults._

object AmmonitePPrintTest extends App {
  println(PPrint(ObjDefinitions.Foo(2, "ab")).mkString)
  println(PPrint(ClsDefinitions.Foo(2, "ab")).mkString)
}

/*
 Fails with Ammonite 0.2.7, and more recent dev versions too
 
[error] .../AmmonitePPrintTest.scala:5: could not find implicit value for evidence parameter of type ammonite.pprint.PPrint[ClsDefinitions.Foo]
[error]   println(PPrint(ClsDefinitions.Foo(2, "ab")).mkString)
[error]                 ^

 */

build.sbt

scalaVersion := "2.11.6"

resolvers ++= Seq(
  Resolver.sonatypeRepo("releases"),
  Resolver.sonatypeRepo("snapshots")
)

libraryDependencies ++= Seq(
  "com.github.alexarchambault" %% "scalacheck-shapeless_1.12" % "0.2.0-SNAPSHOT",
  "com.lihaoyi" %% "ammonite-pprint" % "0.2.7"
)

Definitions.scala

object ObjDefinitions {
  case class Foo(i: Int, s: String)
}

class ClsDefinitions {
  case class Foo(i: Int, s: String)
}

object ClsDefinitions extends ClsDefinitions

ShapelessTest.scala

import org.scalacheck._, Shapeless._

object ShapelessTest extends App {
  val o = Arbitrary.arbitrary[ObjDefinitions.Foo]
  val c = Arbitrary.arbitrary[ClsDefinitions.Foo]

  for (i <- 1 to 10)
    println(o.sample)

  for (i <- 1 to 10)
    println(c.sample)
}

/*
 Succeeds with shapeless 2.2.0-RC4 (through scalacheck-shapeless 0.2.0-SNAPSHOT)
 */