Well, I found a strange bug and I suppose it's caused only in AGS 2.7 because I never had it with AGS 2.62.
Well, it's actually a simple problem, I have 4 objects in my room, but only two show up! I can do what I want, delete all the script that is concerned about the objects, didn't work, deleted all the objects and created them again, it was still there. Even more strange is that it were always the same objects, more precisely, only the same pictures, because the objects numbers were different the next time.
Then I just created a new room with everything the same, the same background and objects, and it worked.
Oh, I forgot to say, "object is initially visible" is on.
I would just use the new room, but I don't want to draw the walkbehinds again....it was quite some work!