The reason for the fork? The other mod made missiles follow slightly wider turning arcs, so they were harder to dodge by going around corners. It seems like a tiny difference, but high-level competitive players want their missiles exactly right because different missile tracking leads to different viable tactics. "That shot into that tunnel is a sure kill" turns into "that shot is unlikely to hit"; "I can dodge that" turns into "I have no option but to run". The primary developer of the other mod was not a high-level competitive player and did not see this as a problem. Merely suggesting the fix (which my wife originally coded as a patch to the other mod), with simulations, a mathematical proof of correctness, and uniformly positive feedback from many top-level pilots, was enough to touch off a flamewar that wasn't settled for weeks.
People can be fanatical about their video games.
[0] the game is Descent (1 and 2). Her mod can be found at https://github.com/CDarrow/DXX-Retro . The other mod is at http://www.dxx-rebirth.com/ . Current competitive 1v1 play is at http://descentchampions.org/ and group play is at http://descentrangers.com .