Yes he says that you can't place an accusative like ʾawlādahum between the muḍāf and the muḍāf ʾilayhi.
Ibn Mujāhid's other student, al-Fārisī says it's "ugly and rare in use".
al-Zamaḫšarī, who is later has a perhaps even more honest version of Ibn Ḫālawayh says.
