This plugin fixes some weapon projectiles colliding incorrectly with the non-solid bounding boxes of certain map objects. This causes them to disappear/explode in mid-air for seemingly no reason.
The issue affects the Wrap Assassin, Bison, Pomson and Dragon's Fury. The Wrap Assassin in particular is very broken (it explodes in your face in the entire last area of badwater, for example)
Here's a recent video by shounic about the issue:
Put projectile_collide_fix.smx in the plugins folder