Something is amiss with deserialization of ListBuffer, as shown here:
import collection.mutable.ListBuffer
import java.io._
val baos = new ByteArrayOutputStream
val oos = new ObjectOutputStream(baos)
oos.writeObject( ListBuffer(1,2,3) )
val bais = new ByteArrayInputStream( baos.toByteArray )
val ois = new ObjectInputStream(bais)
val lb = ois.readObject.asInstanceOf[ListBuffer[Int]]
val lb2 = ListBuffer[Int]() ++= lb
lb2 ++= List(1) // All okay
lb ++= List(1) // Throws an exception for me
Not sure whether this is related to other deserialization bugs (e.g. #SI-5262).