"collect" is not collecting

i have the following:

vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv

object XmlTest {
  import com.codecommit.antixml._
  implicit def toPicker(nodes: Group[Node]): Picker = new Picker(nodes)
  class Picker(nodes: Group[Node]) {    def pick[A <: Node : ClassManifest]: Group[A] = nodes collect {
      case a if implicitly[ClassManifest[A]].erasure.isInstance(a) => a.asInstanceOf[A]
    }
  }
  def testCollect(elems: Group[Elem]) {
    println("size before collect = " + elems.size)
    val es = elems collect {
      case e if e.name == "c" => println("element name is " + e.name); e
    }
    println("size after collect = " + es.size)
  }
  def main(args: Array[String]) {
    val xml = XML.fromString("<a><b/><c/><d/></a>")
    // this works because <a> has only elements as children
    testCollect(xml.children.asInstanceOf[Group[Elem]])
    // pick filters collection by type
    testCollect(xml.children.pick[Elem])
  }
}

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

when i ran it, it printed the following:

[info] size before collect = 3           // size is 3
[info] element name is c                 // element c matches
[info] size after collect = 1              // this is correct
[info] size before collect = 3           // size is the same as the previous case
[info] element name is c                 // element "c" is matched as well
[info] size after collect = 0               // this should be 1

i am at a lost here.  what is going on?

regards,
walter
--
.......__o
.......\<,
....( )/ ( )...



--
.......__o
.......\<,
....( )/ ( )...