Quake engine coders... fix gravity!
From Hannu Kankaanpää's home pages: Now you may be thinking: "baah, I know how to do gravity.." but there's a big flaw in the commonly used Euler's method to handle the gravity (or other forces). Even all the Quake games have this problem. Then what is it? If you have more frames per second in Quake, your player will run faster and jump higher. There are some places in Quake where you can't jump high enough if you don't have enough frames per second. Sounds odd, right?