At one time, Half-Life 2 became one of the most popular games for speedrunning thanks to the physics of the Source engine. However, Valve recently almost ruined the speedrun by releasing a fixed anniversary edition.
We are talking about a loophole in the chapter Route Kanal. In one of the levels, players need to solve a puzzle to collect water in a pool under a grate and dive into a pipe with a red backlight. Initially, it was implied that the sewer pipe would be closed by an «invisible wall» so that gamers could solve the riddle fairly. However, the collision was only in the Xbox 360 version.
The error in the PC version was fixed 20 years later with the release of the anniversary edition of Half-Life 2. But then speedrunners were outraged: it turns out that the bug allowed you to quickly skip the level without solving the puzzle. Valve listened to the fans and recently released another patch with a noteworthy point: «Removed collision from an underwater tube that speed runners enjoy».
However, the anniversary version is still poorly suited for speedrunning. As Rock Paper Shotgun writes, speedrunners continue to use old Half-Life 2 builds, where convenient bugs have been preserved. For example, the ability to squeeze through a wall while carrying another object in front of you.
Earlier, Valve fixed a 17-year-old error in Team Fortress 2, returning the Scout's pants to the desired color. The work was in vain — the bug had to be returned.