#1 is a new style 6P with the tailcap locked out. Notice the gap between the tail and the body.
#2 and #3 are new style 6P tailcaps. These have a "witness" mark that is a little circle near the base of the tailcap. Lining this up with the one on the body can be used to know when the light is locked out and the like. The button on the back should be able to move up and down when the tailcap is off of the light, but the rubber "boot" and the metal inner part should not detach from the black part.
#4 is the tailcap screwed all the way down (the light would be on if the bezel was attached /ubbthreads/images/graemlins/smile.gif)
#5 is an exploded view of the 6P. A is the bezel, B is the lamp assembly (LA), C are the 123 batteries, D is the body, and E is the tailcap.
Does your tailcap look like the one in #2 and #3?
-Mike