If you already blew up the trapped room outside, "Billeh-gar!"the picture will have been destroyed by the explosion. Probably why the chair is also missing from that corner.
I can't remember from the beta whether you can still get the button to appear or not. I may have had to back up to before the explosion. It may just be a perception issue.
That may be the difference between what you're seeing and what people are telling you, though.
