As kranmer said save anywhere could produce scripting failures if used during cutscenes or right before scripted actions. I experienced your exact behaviour. You have to defeat the demon and play trough the entire sequence, till the encampment.
I didn't try, but if you walk to the encampment it could be bossible to "re-synchronize" the script.

Thank you for your answer. I didn't save in a middle of a cutscene, i knew it could cause problems, i just saved in the room, no dialogue, no scene.
Unfortunately, i can't go back, downstairs doesn't work and i have no other save (i know, it was not smart^^'). I think im' gonna try the saving files we can find on gamefaq.
Thanks again for your reply =)

You actually did. It is safe to save when there are no monsters/png on screen and when you already triggered everything, be it an encounter, a chest or a dialogue with a png.
Chronist shows up normally when all is done in the room and only him and your party is visible.

if you save in furnace room just before the telescope one during the short cutscene, you will find yourself wandering there.

That's good to know, thanks again, i won't make this mistake again, be sure about that.
Gamefaq doesn't have the saves files anymore, i think i'm gonna launch a new game (i don't like to use someone else's save, anyway :p)