What's wrong with promises in Grails 3?

Question

Grails

Hey!
Here is a simple example from the official documentation:

def test() {
      def map = new PromiseMap()
        map['one'] = { 2 * 2 }
        map['two'] = { 4 * 4 }
        map['three'] = { 8 * 8 }
        map.onComplete { Map results ->
          render results as JSON
        }
    }

The result is unpredictable and often wrong -
{"one":4,"two":16,"three":64}
Next run -
{"one":16,"two":64,"three":4}
What the fuck? Thank you.