Fixed a bug in server code where we used old damage data for the stat/quest/achievement processing. For example if you hit someone with the ak47, then finish him with a kar98 - you don't get a kar98 kill instead you got an ak47 kill. This made certain achievements massively harder (like pyromantic expert) and that's how we found this bug.
Server Hotfix 0.58.0.4850
Source: Steam Community (opens in a new tab)