A private member in super trait cannot be accessed from sub trait (and sub class)

trait.groovy

trait TraitA {
   def propA = "AAA"
   private privatePropA = "aaa"
   def doA() {
       propA + privatePropA
   }
}
trait TraitB extends TraitA {
   def propB = "BBB"
   def doB() {
       propA + propB
   }
   def doBWithPrivate() {
       privatePropA + propB
   }
}
class Hoge implements TraitB {
}

assert new Hoge().doA() == 'AAAaaa'
assert GroovyAssert.shouldFail(groovy.lang.MissingPropertyException) {
    new Hoge().privatePropA
}.message == "No such property: privatePropA for class: Hoge"

assert new Hoge().doB() == 'AAABBB'
assert GroovyAssert.shouldFail(groovy.lang.MissingPropertyException) {
    new Hoge().doBWithPrivate()
}.message == "No such property: privatePropA for class: Hoge"