Yes I came to post exactly this, and found your comment, so will reply instead. The bug doesn't seem to be obscure. It is there in the right place. Someone thinking about checking "why some players are attacked more often?" would probably choose this as the first place to double check, since it is directly related to selecting the player for attack.

Maybe the most occult part of this is figuring out that the unique IDs assigned to the players play a role.