A problem with Gradle's Instantiator and closures referencing class' private fields

CommandRunner.groovy

import org.gradle.api.Project

class CommandRunner {
    private final Project project

    def CommandRunner(Project project) {
        this.project = project
    }

    public String run(Object... args) {
        def result = new ByteArrayOutputStream().withStream { os ->
            project.exec {
                commandLine args
                standardOutput = os
            }
            os.toString()
        }

        result
    }
}

CommandRunnerTest.groovy

import org.gradle.api.internal.project.ProjectInternal
import org.gradle.internal.reflect.Instantiator
import org.gradle.testfixtures.ProjectBuilder
import org.junit.Test

public class CommandRunnerTest {
    @Test
    public void testName() throws Exception {
        def project = new ProjectBuilder().build()
        Instantiator instantiator = ((ProjectInternal) project).getServices().get(Instantiator)
        def commandRunner = instantiator.newInstance(CommandRunner, project)

        commandRunner.run("echo", "hello world")
    }
}

junit stacktrace

    groovy.lang.MissingPropertyException: Could not find property 'project' on CommandRunner_Decorated@7e32156a.
        at org.gradle.api.internal.AbstractDynamicObject.propertyMissingException(AbstractDynamicObject.java:43)
        at org.gradle.api.internal.AbstractDynamicObject.getProperty(AbstractDynamicObject.java:35)
        at org.gradle.api.internal.CompositeDynamicObject.getProperty(CompositeDynamicObject.java:94)
        at CommandRunner_Decorated.getProperty(Unknown Source)
        at org.codehaus.groovy.runtime.InvokerHelper.getProperty(InvokerHelper.java:168)
        at groovy.lang.Closure.getPropertyTryThese(Closure.java:321)
        at groovy.lang.Closure.getPropertyOwnerFirst(Closure.java:315)
        at groovy.lang.Closure.getProperty(Closure.java:304)
        at org.codehaus.groovy.runtime.callsite.PogoGetPropertySite.getProperty(PogoGetPropertySite.java:47)
        at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callGroovyObjectGetProperty(AbstractCallSite.java:231)
        at CommandRunner$_run_closure1.doCall(CommandRunner.groovy:12)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:606)
        at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:90)
        at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:324)
        at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeMethod(ClosureMetaClass.java:278)
        at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1016)
        at groovy.lang.Closure.call(Closure.java:423)
        at groovy.lang.Closure.call(Closure.java:439)
        at org.codehaus.groovy.runtime.IOGroovyMethods.withStream(IOGroovyMethods.java:1298)
        at org.codehaus.groovy.runtime.dgm$731.invoke(Unknown Source)
        at org.codehaus.groovy.runtime.callsite.PojoMetaMethodSite$PojoMetaMethodSiteNoUnwrapNoCoerce.invoke(PojoMetaMethodSite.java:271)
        at org.codehaus.groovy.runtime.callsite.PojoMetaMethodSite.call(PojoMetaMethodSite.java:53)
        at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:45)
        at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:108)
        at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:116)
        at CommandRunner.run(CommandRunner.groovy:11)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:606)
        at org.codehaus.groovy.runtime.callsite.PogoMetaMethodSite$PogoCachedMethodSite.invoke(PogoMetaMethodSite.java:166)
        at org.codehaus.groovy.runtime.callsite.PogoMetaMethodSite.call(PogoMetaMethodSite.java:68)
        at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:45)
        at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:108)
        at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:120)
        at CommandRunnerTest.testName(CommandRunnerTest.groovy:14)