I am not completely sure if this is the right place to ask as I don't know for sure if it is caused by KDE. But I know that on my system it occurs only when I am in KDE: The Ctrl and Shift key are persistent, i.e. if I press either of them and release it again the next keyboard input is taken as if this key is still pressed. For example Shift -> release Shift -> a will print a capital A in any GUI. This does not happen if I start just X and e.g. the xterm. I find this behavior very annoying and would like to know how to disable it in KDE. As far as I remember I didn't have it with the initial KDE installation on my system but some-when it appeared. Now I am running the latest KDE 4.9.

Thanks in advance!

The most obvious cause for this would be because sticky keys have been enabled. Does this behaviour only occur if you hold Shift or Ctrl down for some time, or do you just tap them and they immediately get stuck? If it's the first one, you've got sticky keys enabled. I don't know the cause if it's the second one, sorry.

Disabling sticky keys should be possible through System Settings->Accessibility (unless it's changed in 4.9, which I think is unlikely). Click the Modifer Keys tab and untick "use sticky keys" if it's ticked.

You were right, sticky keys were enabled. I never consciously enabled this feature but it is conceivable that it some-when appeared since I am keeping the same configuration files since many kde versions.