Which is going to make it extremely difficult to reproduce and fix. I would recommend that some extensive testing be carried out. You will need to ensure a clean environment...Ie Clean installs of stock BZ2. No hackers, ddossers or laggers in the game. Probably be best to do it "in the Dark" (off raknet) so that Idiots don't know that you are doing it. Turn off the fight, build ships and shoot at each other, see if any other game functions combine to cause it, like building stuff at the same time or particular graphic settings. Does it happen with the AI? Try it with logging on and logging OFF. This sort of bug can be really really hard to pin down, trying to do it and "play" at the same time will be almost impossible....and think it's double damage. This is sporadic and impossible to replicate consistently.
And to be honest, if certain notorious players were in the games where this has been seen then I would be inclined to disregard it as evidence of a bug at all and just assume it is just yet another hacking attempt.
Reminds me of the old "Claws double sp and blast" incident...invisible shots...sudden extra damage...