Compilation failed on sealed trait with method

[LMnet]

Here is the example of code:

@pushka
sealed trait OperationData {
  def length: Int
}

object OperationData {

  case object Void extends OperationData {
    def length: Int = 0
  }

  case class Str(value: String) extends OperationData {
    def length: Int = value.length
  }

}

Compilation error:

[error] /home/lmnet/Work/Projects/involve/shared/src/main/scala/involve/domain/OperationData.scala:5: value _rw is not a member of object involve.domain.OperationData.Str
[error] @pushka
[error]  ^

Reproducable on 0.3.0 and 0.3.1 versions.