The lesson seems to indicate that this separation is 'allowed' but 'irregular'.
However it seems frequent and intrinsic enough in some translations to deserve identifying and defining as a rule of syntax.
If the 'possession' is the 'object' of the verb in the following clause then it is separated from dont and put after the verb in that clause. 'Dont' here is like a relative pronoun joining two clauses. All the examples support this observation.
Tu as jeté la chaussure dont le talon est cassé.You threw away the shoe with the broken heel [lit. whose heel is broken]
BUT???Tu as jeté la chaussure chère dont j'ai cassé le talon.
Les enfants, dont je connais la maman, sont bien élevés.
François, dont j'ai rencontré la femme le mois dernier