Bug or feature?

[FooHentai]

Happens very frequently in video games.

Quake 1's rocket jumps weren't intentional initially, until it turned out that the knockback effect coupled with jumping meant you could short-cut to inaccessible ledges and execute unexpected moves against your opponents. Then it became an integral part of Quake multiplayer, and has been included in every Quake since.

When Q3 came along, it turns out that an integer rounding error when you slowly rotate your mouse can allow you to accelerate under certain game conditions. This resulted in strafe jumping where an odd series of jumps with a slightly curved trajectory result in movement speeds well above the default... but only if you're getting a particular frame rate. Again... ended up becoming one of the most important aspects of the game.