Chantiri

This has probably been answered before, but I can't find anything on it. Does this happen to anyone else? I'm walking through a forest or though a building when suddenly I'm underground or within the wall structure. It isn't a hidden trapdoor or anything, but I've just gone between the 'panels' (or whatever) that make up the scenery. Is it my avatar? Is it the scenery? Is there a way to stop it? To get out, I usually have to teleport somewhere else. Thankyou.