Don't use markers for raycast
While the markers are not displayed and not colliding with the player, they are still used for raycasts. Example: You can't activate a door if it's behind a marker. Marker objects should not be inserted in the physics world at all.
(RM-431 from redmine: created on 2012-10-24 by scrawl ., , closed on 2012-10-24 by scrawl .)