Thank you for your answer Zed.
I found out friday night what was the origin of the problem.
It’s the “WP-Properties” addon that overwrite the css of a part of the frontpage, so it makes disapear this text. I totaly forgot to disable this one when I was trying your troubleshooting guide 😐
As i were away for the weekend, i couldn’t send a message saying that problem is now partially solved (in fact, when i “deactivate” (or more precisely, when i change some stuff on the presentation) the default WP-Properties’ css, there is now another problem, but only in “properties”, so i’m working on it).