I'm pretty sure that I'm right about the the o-ring design change being the culprit.
Charlie posted an exploded view of the Lion cub in
LIONCUB UPDATE THREAD - PT. 2 (1st post, second picture).
The o-ring for the LC body is positioned on the body, just past the threads. Replace the LC body with a LionHeart body and the o-ring is effectively lost. I'd say that qualifies for less than optimal! /ubbthreads/images/graemlins/icon15.gif
It also explains the visible difference in the fit, as shown in the picture you referenced. I bet the gap in the LH head/LC body combo is caused by the LH head having the o-ring up by the board, along with the LC o-ring on the body. I think the gap is actually showing us the LC's black o-ring in the LH head/ LC body combo.
Of course, it would be a simple matter to put an o-ring on a LionHeart body to regain water resistance, but would the light work then? And how long with the o-ring last if it was sitting on the threads, being compressed?
Darn those design improvements! /ubbthreads/images/graemlins/grin.gif