Metaclass not cleaned up when running unit tests in interactive mode

@TestFor(Book)
class BookTests {

    void testMetaClassOnce() {
        assert !Book.metaClass.hasMetaMethod('foo')

        Book.metaClass."static".foo = {-> 'bar' }

        assert Book.metaClass.hasMetaMethod('foo')
        assert Book.foo() == 'bar'
    }

    void testMetaClassTwice() {
        assert !Book.metaClass.hasMetaMethod('foo')

        Book.metaClass."static".foo = {-> 'bar' }

        assert Book.metaClass.hasMetaMethod('foo')
        assert Book.foo() == 'bar'
    }
}

grails> test-app unit:
| Completed 2 unit tests, 0 failed in 2526ms
| Tests PASSED - view reports in target/test-reports
grails> test-app unit:
| Running 2 unit tests... 1 of 2
| Failure:  testMetaClassOnce(metaclasstest.BookTests)
|  Assertion failed: 

assert !Book.metaClass.hasMetaMethod('foo')
       |     |         |
       false |         true
             groovy.lang.ExpandoMetaClass@241ee2c5[class metaclasstest.Book]

	at metaclasstest.BookTests.testMetaClassOnce(BookTests.groovy:9)
| Running 2 unit tests... 2 of 2
| Failure:  testMetaClassTwice(metaclasstest.BookTests)
|  Assertion failed: 

assert !Book.metaClass.hasMetaMethod('foo')
       |     |         |
       false |         true
             groovy.lang.ExpandoMetaClass@241ee2c5[class metaclasstest.Book]

	at metaclasstest.BookTests.testMetaClassTwice(BookTests.groovy:18)
| Completed 2 unit tests, 2 failed in 186ms
| Tests FAILED  - view reports in target/test-reports