Separate compilation goes wrong with private object or private lazy val in trait

[smarter]

A_1.scala:

trait A {
  val foo = 0 + x
  private lazy val x = 1
}

B_2.scala:

object B extends A {
  def main(args: Array[String]): Unit = {
    println(foo)
  }
}

% ./bin/dotc A_1.scala
% ./bin/dotc B_2.scala
% scala B
java.lang.NoSuchMethodError: A.A$$x()I
        at B$.<init>(B.scala:1)
        at B$.<clinit>(B.scala)
        at B.main(B.scala)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:497)
        at scala.reflect.internal.util.ScalaClassLoader$$anonfun$run$1.apply(ScalaClassLoader.scala:70)
        at scala.reflect.internal.util.ScalaClassLoader$class.asContext(ScalaClassLoader.scala:31)
        at scala.reflect.internal.util.ScalaClassLoader$URLClassLoader.asContext(ScalaClassLoader.scala:101)
        at scala.reflect.internal.util.ScalaClassLoader$class.run(ScalaClassLoader.scala:70)
        at scala.reflect.internal.util.ScalaClassLoader$URLClassLoader.run(ScalaClassLoader.scala:101)
        at scala.tools.nsc.CommonRunner$class.run(ObjectRunner.scala:22)
        at scala.tools.nsc.ObjectRunner$.run(ObjectRunner.scala:39)
        at scala.tools.nsc.CommonRunner$class.runAndCatch(ObjectRunner.scala:29)
        at scala.tools.nsc.ObjectRunner$.runAndCatch(ObjectRunner.scala:39)
        at scala.tools.nsc.MainGenericRunner.runTarget$1(MainGenericRunner.scala:65)
        at scala.tools.nsc.MainGenericRunner.run$1(MainGenericRunner.scala:87)
        at scala.tools.nsc.MainGenericRunner.process(MainGenericRunner.scala:98)
        at scala.tools.nsc.MainGenericRunner$.main(MainGenericRunner.scala:103)
        at scala.tools.nsc.MainGenericRunner.main(MainGenericRunner.scala)

Here's what A.class looks like when we compile A_1.scala and B_2.scala together:

public interface A {
    default public void $init$() {
    }

    public int foo();

    default public int initial$foo() {
        return 0 + this.A$$x();
    }

    default public int A$$x() {
        return 1;
    }
}

and here's what it looks like when we just compile A_1.scala:

public interface A {
    default public void $init$() {
    }

    public int foo();

    default public int initial$foo() {
        return 0 + this.x();
    }

    default private int x() {
        return 1;
    }
}

(Decompilation done using http://www.benf.org/other/cfr/)