If you try to switch your teleport type with an object out (right click) but are looking at an object that would cause an arm swing you'll teleport either through the wall or on top of the block.

E.g. Try to open door with right click causes you to open the door and teleport through the now open door, or to the top of the block outside the door (depending on your current setting)

Moved: http://redmine.sk89q.com/issues/82