Problem with @CompileStatic, SpreadOperator and calling a function

GroovySpreadOperatorTest.groovy

package pl.klkl

import groovy.transform.CompileStatic
import spock.lang.Specification

class GroovySpreadOperatorTest extends Specification {

    interface Service {
        List<Integer> heavyOperation()
    }

    @CompileStatic
    List<String> invokeCompileStatic(Service service){
        service.heavyOperation()*.toString()
    }

    List<String> invoke(Service service){
        service.heavyOperation()*.toString()
    }

    //This test is failing. heavyOperation is called twice.
    def "should be called once - with compile static"() {
        given:
            Service external = Mock(Service)
            1 * external.heavyOperation() >> [0]
        when:
            def result = invokeCompileStatic(external)
        then:
            result == ["0"]

    }

    def "should be called once - without compile static"() {
        given:
            Service external = Mock(Service)
            1 * external.heavyOperation() >> [0]
        when:
            def result = invoke(external)
        then:
            result == ["0"]
    }
}