% scalac29 -Xprint:jvm -unchecked test/files/run/t7268.scala && scala29 Test
test/files/run/t7268.scala:34: warning: non variable type-argument T in type pattern scala.collection.mutable.WrappedArray[T] is unchecked since it is eliminated by erasure
      case xs: WrappedArray[T] =>
               ^
[[syntax trees at end of jvm]]// Scala source: t7268.scala
package <empty> {
  final object Test extends java.lang.Object with ScalaObject {
    def main(args: Array[java.lang.String]): Unit = {
      val test: ArrayWrapper = new ArrayWrapper(reflect.this.Manifest.Double());
      test.update(scala.this.Predef.wrapDoubleArray(Array[Double]{1.0}));
      test.updateOne(scala.Double.box(1.0))
    };
    def this(): object Test = {
      Test.super.this();
      ()
    }
  };
  class ArrayWrapper extends java.lang.Object with ScalaObject {
    private[this] val array: java.lang.Object = _;
    <stable> <accessor> def array(): java.lang.Object = ArrayWrapper.this.array;
    def updateOne(elem: java.lang.Object): Unit = ArrayWrapper.this.update(scala.this.Predef.genericWrapArray(Array[java.lang.Object]{elem}));
    def update(elems: Seq): Unit = ArrayWrapper.this.updateAll(elems);
    def updateAll(elems: Traversable): Unit = {
      scala.this.Predef.println(elems.getClass());
      {
        <synthetic> val temp1: Traversable = elems;
        if (temp1.$isInstanceOf[scala.collection.mutable.WrappedArray]())
          {
            <synthetic> val temp2: scala.collection.mutable.WrappedArray = temp1.$asInstanceOf[scala.collection.mutable.WrappedArray]();
            val xs: scala.collection.mutable.WrappedArray = temp2;
            scala.this.Predef.println(xs.array());
            runtime.this.ScalaRunTime.array_update(ArrayWrapper.this.array(), 0, runtime.this.ScalaRunTime.array_apply(xs.array(), 0));
            java.this.lang.System.arraycopy(xs.array(), 0, ArrayWrapper.this.array(), 0, xs.length());
            scala.this.Predef.println("== ok ==")
          }
        else
          {
            ()
          }
      }
    };
    def this(implicit evidence$1: scala.reflect.ClassManifest): ArrayWrapper = {
      ArrayWrapper.super.this();
      ArrayWrapper.this.array = evidence$1.newArray(2);
      ()
    }
  }
}

one warning found

class scala.collection.mutable.WrappedArray$ofDouble
[D@518f5824
== ok ==
class scala.collection.mutable.WrappedArray$ofRef
[Ljava.lang.Object;@19e3cd51
java.lang.ArrayStoreException
	at java.lang.System.arraycopy(Native Method)
	at ArrayWrapper.updateAll(t7268.scala:42)
	at ArrayWrapper.update(t7268.scala:25)
	at ArrayWrapper.updateOne(t7268.scala:20)
	at Test$.main(t7268.scala:9)
	at Test.main(t7268.scala)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:597)
	at scala.tools.nsc.util.ScalaClassLoader$$anonfun$run$1.apply(ScalaClassLoader.scala:78)
	at scala.tools.nsc.util.ScalaClassLoader$class.asContext(ScalaClassLoader.scala:24)
	at scala.tools.nsc.util.ScalaClassLoader$URLClassLoader.asContext(ScalaClassLoader.scala:88)
	at scala.tools.nsc.util.ScalaClassLoader$class.run(ScalaClassLoader.scala:78)
	at scala.tools.nsc.util.ScalaClassLoader$URLClassLoader.run(ScalaClassLoader.scala:101)
	at scala.tools.nsc.ObjectRunner$.run(ObjectRunner.scala:33)
	at scala.tools.nsc.ObjectRunner$.runAndCatch(ObjectRunner.scala:40)
	at scala.tools.nsc.MainGenericRunner.runTarget$1(MainGenericRunner.scala:56)
	at scala.tools.nsc.MainGenericRunner.process(MainGenericRunner.scala:80)
	at scala.tools.nsc.MainGenericRunner$.main(MainGenericRunner.scala:89)
	at scala.tools.nsc.MainGenericRunner.main(MainGenericRunner.scala)

% cat test/files/run/t7268.scala import scala.collection.mutable.WrappedArray
//import scala.reflect.ClassTag

object Test {

  def main(args: Array[String]) {
    val test = new ArrayWrapper[Double]
    test.update(1.0)    // ok
    test.updateOne(1.0) // failure with ArrayStoreExcpetion
  }
}

class ArrayWrapper[T: ClassManifest] {
  val array = new Array[T](2)

  // elem will be boxed to java.lang.Object (java.lang.Double), then wrapped as
  // Array[Object] and passed to scala.LowPriorityImplicits.genericWrapArray[T](xs: Array[T])
  // becaues of update(elems: T*), and causes ArrayStoreException.
  def updateOne(elem: T) {
    update(elem)
  }

  // ok when called outside directly
  def update(elems: T*) {
    updateAll(elems)
  }

  def updateAll(elems: scala.collection.Traversable[T]) {
    println(elems.getClass)
    // class scala.collection.mutable.WrappedArray$ofDouble -- when via update
    // class scala.collection.mutable.WrappedArray$ofRef    -- when via updateOne

    elems match {
      case xs: WrappedArray[T] =>
        println(xs.array)
        // [D@504ad009                  --- when via update
        // [Ljava.lang.Object;@3b87bd31 --- when via updateOne

        array(0) = xs.array(0)
        // ok

        System.arraycopy(xs.array, 0, array, 0, xs.length)
        // ok             --- when via update
        // failure with java.lang.ArrayStoreException --- when via updateOne

        println("== ok ==")
      case _ =>
    }
  }
}

// File: build.sbt
scalaVersion := "2.10.1"

// File: src/main/scala/bug/Bug.scala
package bug

class Foo(val args: Any*)
case class Bar(id: Int) extends Foo(id)

object Bug extends App {
  val msg = Bar(666)
  val id  = msg.id // boom!
}

[error] (run-main) java.lang.ClassCastException: 
  scala.collection.mutable.WrappedArray$ofRef cannot be cast to java.lang.Integer
java.lang.ClassCastException: scala.collection.mutable.WrappedArray$ofRef cannot be 
  cast to java.lang.Integer
    at scala.runtime.BoxesRunTime.unboxToInt(Unknown Source)
    at bug.Bar.id(Test.scala:4)
    at bug.Bug$delayedInit$body.apply(Test.scala:8)
    at scala.Function0$class.apply$mcV$sp(Function0.scala:40)
        ...

import scala.collection.immutable.ArraySeq
import scala.reflect.ClassTag

object Test {

  def main(args: Array[String]): Unit = {
    val test = new ArrayWrapper[Double]
    test.update(1.0)    // ok
    test.updateOne(1.0) // failure with ArrayStoreExcpetion
  }
}

class ArrayWrapper[T: ClassTag] {
  val array = new Array[T](2)

  // elem will be boxed to java.lang.Object (java.lang.Double), then wrapped as
  // Array[Object] and passed to scala.LowPriorityImplicits.genericWrapArray[T](xs: Array[T])
  // becaues of update(elems: T*), and causes ArrayStoreException.
  def updateOne(elem: T): Unit = {
    update(elem)
  }

  // ok when called outside directly
  def update(elems: T*): Unit = {
    updateAll(elems)
  }

  def updateAll(elems: scala.collection.Traversable[T]): Unit = {
    println(elems.getClass)
    // class scala.collection.mutable.WrappedArray$ofDouble -- when via update
    // class scala.collection.mutable.WrappedArray$ofRef    -- when via updateOne

    elems match {
      case xs: ArraySeq[T] =>
        println(xs.unsafeArray)
        // [D@504ad009                  --- when via update
        // [Ljava.lang.Object;@3b87bd31 --- when via updateOne

        array(0) = xs.unsafeArray(0).asInstanceOf[T]
        // ok

        System.arraycopy(xs.unsafeArray, 0, array, 0, xs.length)
        // ok             --- when via update
        // failure with java.lang.ArrayStoreException --- when via updateOne

        println("== ok ==")
      case _ =>
    }
  }
}