This is a bug report that I cannot see any obvious place to post – there does not seem to be a forum section for keyboard/mouse.

Just got the KM746 bundle and while most things are behaving as expected, there is a lag on the keyboard when any modifier key, e.g. Shift/Ctrl, is held down. This is resulting in uppercase characters/punctuation ending up in the wrong order or being omitted entirely when I am typing quickly. I have tested on both Windows and iOS and the behaviour is even worse over Bluetooth than when using the receiver, so I suspect the keyboard's firmware is causing it (it is definitely nothing to do with any accessibility features on Windows as posited elsewhere). Have updated the firmware to the latest version using DDPM and the issue is still present.

If it can't be resolved then I will have to return the product as it is essentially useless to me like this.