Thank you for your reply.
This bug persists both on houses with Sims and on empty houses. Every time I click on an empty house to switch to Construction Mode, I hear the "click" as if I had clicked on the button to lower the walls. When I put the walls back up, if I click on a button, they lower themselves. I just don't get it. It's as if the game has "memorized" that high walls are forbidden.
P.S: I don't think a screenshot will help for this case, maybe a video but I don't know if I can post it here.
(Sorry for my english, I'm french)