Broken enum equality (with powermock)

With this enum:

public enum Testnum {
    A("a"), B("b");

    String x;

    private Testnum(String x) {
        this.x = x;
    }
}

The assertFalse in this test fails:

import static org.junit.Assert.assertFalse;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.powermock.api.mockito.PowerMockito;
import org.powermock.core.classloader.annotations.SuppressStaticInitializationFor;
import org.powermock.modules.junit4.PowerMockRunner;

@RunWith(PowerMockRunner.class)
@SuppressStaticInitializationFor("Testnum")
public class EnumTest {

    @Test
    public void mainSuccess() {
        PowerMockito.mockStatic(Testnum.class);

        assertFalse(Testnum.A == Testnum.B);
    }
}

Any idea why / how I can work around this?