Nikolay Sivov (@nsivov) commented about dlls/mf/tests/transform.c:
ret = IMFSample_Release(output_sample); ok(ret == 0, "Release returned %lu\n", ret);
hr = IMFTransform_GetInputStatus(transform, 0, &flags);
ok(hr == S_OK, "Got %#lx\n", hr);
ok(flags == MFT_INPUT_STATUS_ACCEPT_DATA, "Got flags %#lx.\n", flags);
Please reset flags before the call.