You guys should reconsider using Z and X for default controls

[Shadow Administrator Drei]

What you're looking for, term-wise, is ghosting/jamming. Keyboards usually don't have their keys as individual electrical switches, but instead groups that, when n within the same group are pressed, cause a short and a report of a non-pressed key. This has been "fixed" by most keyboards just reporting nothing when this is detected. It is on a cheap keyboard - and sometimes solvable by modifying the HID settings - that this happens. The thing is, it is a super common money-saving carry-over in designs that even moderate cost keyboards have this issue. You can never know how every possible keyboard is going to work; however, so it isn't something you can solve except by good practices. You should try to implement forcing the setup of defaults on first launch or a quick swap available to a more varied option on top of allowing the customizing of the hotkeys.