This video shows the now-patched bug that caused character hitboxes to sometimes go significantly out of sync with character models in Team Fortress 2.
These days, we're all used to games getting important post-launch patches that fix bugs and change gameplay balance issues that were present in the initial release. Usually, though, it doesn't take an entire decade for a major bug to be noticed and fixed in a popular game. That is what seems to have happened this week in Team Fortress 2, though.
Over on Reddit, user sigsegv__ lays out how the game would often get confused when a player switched between certain sets of characters in the middle of a match. Apparently, after switching from the soldier/pyro/demo/engineer/medic/spy to the scout/heavy/sniper (or vice versa), the character hitbox (that polygonal mesh that determines what area can be hit by a bullet) would start moving significantly out of sync with the visual character model that opponents could see on the server. This video illustrates the problem pretty clearly, showing character and hitbox animations that are well out of step.
The problem itself stems from a pretty arcane bit of code having to do with the differing orders that "pose parameters" are stored for these sets of character classes. Once identified, the fix involved changing only a single line of code, though as sigsegv__ notes, "knowing which one line of code is missing, and where, is the difficult part, you might say."
from After 10 years, this significant Team Fortress 2 bug has been fixed