wcm io AemContextExtension mocking LanguageManager in JUnit 5

I just upgraded our AEM codebase to use JUnit 5 but we are having some issues with some tests mocking specific methods of the LanguageManager.

@MockitoSettings(strictness = Strictness.LENIENT)
@ExtendWith({AemContextExtension.class, MockitoExtension.class})
public class SomeComponentTest {

    @Mock
    private LanguageManager languageManager;

    @BeforeEach
    public void setUp() throws Exception {
        ...
        context.registerService(LanguageManager.class, languageManager);
        ...
    }


    @Test
    public void someTest() {
        ...
        Page mockPage = mock(Page.class);
        given(languageManager.getLanguageRoot(any())).willReturn(mockPage);
        ...
    }
}

Even though I register the LanguageManager mock it still seem to get the WCM IO provided mock, which is initialized here: https://github.com/wcm-io/wcm-io-testing/blob/develop/aem-mock/core/src/main/java/io/wcm/testing/mock/aem/context/AemContextImpl.java -> registerInjectActivateService(new MockLanguageManager());

Am I doing something wrong here or is there just no way to spy / mock the methods of the LanguageManager. Do note that in the past this worked when using:

@RunWith(MockitoJUnitRunner.class)