Bon, voici la règle.

Question

I've read all the comments here and in the related links, several times.
It seems the rule be stated as, there's NO gender/number agreement of the participle when there is a direct object following the verb.
Ça vous dit ?

Accepted Answer

Bonjour Lewis,
Yes, that's correct! We have not published a lesson on this specific grammar point. It is on our to-do list though!
@Maarten, how interesting and random! I found out about this very particular TED talk only about 2 weeks ago (and yet, these two teachers started this show at least three years ago)! Just like Chris, it made myself (as well as the rest of the language team) laugh a lot ;-). It's very interesting grammatically speaking and so funny at the same time!
Bonne journée !

Answer

Not a direct answer but you might enjoy this TED talk on French - from about 6 min 30 sec, or a bit after, is a fantastic demonstration of a very plausible reason that there is no past participle agreement unless the direct object precedes the compound verb. The whole video and this section in particular is very entertaining !

https://www.ted.com/talks/arnaud_hoedt_jerome_piron_la_faute_de_l_orthographe?language=fr

Answer

Je me suis bien amusé! :)))