This video and post is a really good example of how to help when you’re experiencing an issue. Thanks to /u/el_vper for putting in the work to identify reproducible steps for this bug (thanks also to /u/Harizio for providing a bind that consistently produces the effect). We’re able to reproduce it here too, and we’re working on a fix.
Providing clear reproducible steps is the best way to track down elusive bugs, and is much more likely to result in a solution than describing an issue out of context. With that in mind, we’d like to address some questions that have come up recently.
Q: Why has hit registration been a problem over the past week?
Some of you have been reporting hit registration issues starting in the past week or so, but we haven't shipped any code recently that would have impacted either hit registration or the way any individual weapons work. That’s not to say that there isn’t a problem, but if it’s new, it's probably not coming from a bug in the game. We're investigating, but in the meantime it helps us when you post reproducible steps that lead to poor hit registration.
Q: I see a bullet decal behind a player, but I didn’t hit them. What happened?
If you take a shot when running, jumping, or when unscoped with an AWP, your inaccuracy will be high and the bullet trace on the server and client are not guaranteed to hit in the same spot. This is because several months ago we shipped an update that eliminated most common aiming cheats, where we separated the client and server's random seed used to determine how inaccuracy is applied to a bullet.
Blood effects will always come from a server message confirming that you hit someone, but bullet impact decals on the world come from your client. Impact decals on the world come from the client because when those impact effects are delayed (as they would be coming from the server), they feel laggy, the game looks and feels unresponsive and it’s more difficult to control recoil.
When your inaccuracy is lowest for a weapon (i.e., when you’re standing still), at most the client and server will diverge by the weapon’s standing inaccuracy. But when you have higher inaccuracy, bullet decals are inaccurate and are not useful feedback. For example, with high inaccuracy bullet decals are not useful in diagnosing whether or not you should have hit someone.
Similarly, when you use sv_showimpacts, any client-reported hit is inaccurate for exactly the same reason. In the past, client-reported hits provided valuable information, but now they’re simply misleading. We’re considering removing the client portion of sv_showimpacts in the future because it literally has no benefit to the player to see this data other than to provide misinformation.
Q: What's the deal with hitboxes?
We mentioned recently that we're working on resolving cases where a player's hitbox doesn't match their model (e.g., jumping, while planting, on ladders, etc.). We have a good idea of how to solve the problem, but the implementing the solution takes time. So we’re working on it, but still don't have an ETA.
As a closing note, we know that some of you are concerned about hit-registration at LAN events (e.g., upcoming ESL One Cologne). There’s no reason to expect that there would be any new bug or issue at these events compared to previous ones.
Ultimately, the majority of hit-registration issues (outside of the planting/jumping/climbing issues we’re currently fixing) are the result of ping, internet connection issues, and the trade-offs that have to be made when connecting multiple players (Source Multiplayer Networking). The best way to avoid these issues is to play on LAN, but the unfortunate reality is that as long as most of us are playing online, some amount of hit-registration issues will be unavoidable.
For any issues that are not the result of these unavoidable factors, the most helpful thing you can do is to provide clear reproducible steps.