Yup, just about everyone reading this who hasn't purposefully bought a keyboard knowingly that is designed specifically to not exhibit this problem is almost certainly using a keyboard that does exhibit this problem. :) Most people just don't know it. :)

Most people don't normally notice the problem because it only occurs when you press multiple keys at the same time that are normally never pressed at the same time and expect them to all register with the software being used, which is not something people usually do except in video games, and in games it isn't something that one would often notice either. The symptom might be playing an intense ARPG and trying to cast several spells while dancing all over the keys possibly while holding one or two modifiers down, or similar in an FPS. If you hit just the right combination of keys on your specific keyboard which do not all independently register then one or more of the things you were trying to tell the game to do might not register, so that one spell might not cast, or you might not run, or you might not move to the right, but a fraction of a second later you're pressing different keys and if something went wrong you might not notice at all, or you might think "shit, I swear I cast that spell..."

So the symptoms are not always identifiable when they happen, particularly because one's attention is kept pretty busy in the game.

I just tested some keypresses to try to repro a ghosting issue and I found one on my keyboard. If I press and hold down SHIFT and then press W, D simultaneously then also press S, the S is ignored. You wouldn't normally press W and S together in an FPS or other game that uses WASD for movement, as that's going forward and backward at the same time while also moving right - but you might press all of those keys on occasion unintentionally but meaning for the last key to actually do something.

I also just tried W+A+Q and that doesn't work either. So if I were running forward and to the left and pressed Q to cast a spell in say... The Witcher 3 - the spell would not get cast. That's a good example of the ghosting problem interfering with a game. :)

It's kind of like figuring out a Fatality move in a Mortal Kombat game. You randomly mash a dozen buttons until something special happens, then wonder what buttons you pressed and/or held in what order. If you figure it out you know the magic combo key to do the fatality move. :) Also, the problem varies from keyboard to keyboard so some combination that doesn't work for one person might work for another, but the other person may have a combo that fails that doesn't for someone else. :)

One way to test for it is to use those WASD keys holding 2 of them down that you might actually use together in a game, any two of them - then with your other hand, press all the keys around them that do something to see if they register, like I did above. Of course, using two hands is kind of cheating, but that's just to make it easier to find the keys that wont work properly. Whether they are something you'd use with one hand while gaming is another aspect. But the problem is still legitimate even with two hands. Perhaps one is running forward and to the left, and uses their other hand to hit the inventory key or a map or some other function and it doesn't work. The thing is we're not likely to notice specifically while playing because what our left hand is doing is jumping all over the keys as we move around, so the problem will be short little bursts of more likely to happen or less likely, and depends on what other keys we hit.

I dunno of a list of keyboards where the issue isn't present at all but you might want to search for "full anti-ghosting gaming keyboard" or something like that. Some of them do full anti-ghosting and others just partial on the left half of the keyboard commonly used for FPS/RPG/RTS/MMO games.

The problem can be noticed in some games which support single-keyboard multiplayer.

I always had this problem with metroid-like games. I only can run and shoot diagonaly when I run left (with left arrow key). When I run right I can´t shoot diagonaly. I didn´t know that this is a common problem. I always thought it occurs because of my wireless keyboard.

I've never really had a problem with ghosting except when playing fighting games, contrary to popular belief keyboard is one of the best control methods for playing fighting games, assuming you aren't playing characters that require 360 inputs.

It is not anything new. I remember my no so cheap keyboard in 1999 having this problem.
As for "very cheap" keyboard with no ghosting - no such thing exists now. Even entry level gaming keyboards only prevent ghosting in WASD block and the best you get in with more expensive ones is usually a 6 key rollover on USB. The cheapest that gets the work done that I know is Microsoft SideWinder X4 and that's hardly cheap.

The rate at which the keyboard reads its keys has nothing to do with ghosting. Ghosting is caused by the ways the individual keys are wired inside of the keyboard. In most keyboards they are connected in a matrix structure which allows for a fairly simple and cheap circuitry, but makes it impossible to detect certain key combinations of multiple nearby keys and can even result in the keyboard submitting keycodes for keys that are not actually pressed.

The double shift key test may nor be the best one because it's just some combinations of keys that work and not others. Modifier keys usually cause least problems. The better test would be something like pressing "tyuio" simultaneously. You would definitely notice the problem if you moved from WASD to NumPad - for example Logitech G105 (which is technically a gaming keyboard) can't even handle a combination like NumPad 6 + NimPad 8 + Space, but handles WASD combinations without problems.
And it makes a difference in fighting games to the point whether the game is playable or not.

The keyboards without this problem exist but these are the more expensive mechanical keyboards. The feature is called N-key rollover (some offer only 6 key rollover, which is enough most of the time). Full N-key rollover on USB requires firmware solutions as far as I know (like in the case of My CM QuickFire), doing this "legally" requires PS/2 port.

Heh: you'll spend a little money, you'll get crappy hardware whatever the deal looks "gold" to you.

Ahh, so "ghosting" is the reason why combos in a game like Magicka may not register. The game mainly uses A,S,D,F,Z,X,C,V and sometimes when the action is tense you need to press the keys down quickly, sometimes hitting 2 or three keys at the same time.

BTW my results with both shift keys pressed down are "ABDEFGHIJKLNOPQRSUW" just like skeletonbow

I still consider 1999 somewhat recent lol

So, just to clarify: Is there a keyboard in existence without any ghosting?

EDIT: What´s with this one: Razer DeathStalker Ultimate? Something with this name must be good.

Isn't it hilarious that not only having the same layout as a typewriter they have managed to copy some of it's flaws as well with this ghosting/key blocking.

I have a Medion keyboard, its pretty cheap and as far as I know it doesn't have any ghosting.

I can't play Binding of Isaac anymore because of this. It worked well when I used a laptop for some reason.