In Kubuntu/Ubuntu (and presumably Debian and other derivatives), the CTRL + ALT + F4 (or any other function key) keyboard shortcut switches from the desktop to a virtual terminal while CTRL + ALT + F7 brings you back to the desktop. However, I want to disable this as it's messing up my HTPC thanks to its dodgy remote control. While I could find a solution for Gnome/Ubuntu readily enough, KDE/Kubuntu was not immediately apparent.
The thing with Kubuntu ("Trusty" 14.04 in my case) is that it tends to replace or hide KDE's apps with its own custom versions. In particular, system configuration apps are often sequestered away in some hole while a friendlier (eye-of-the-beholder) Kubuntu version replaces it in the system settings control panel or similar. The Kubuntu "Shortcuts and gestures" app did not have any option to disable the CTRL + ALT + Fn Key shortcuts. Using it to perhaps override the shortcut by assigning it to a more innocent operation like "clear clipboard" didn't work because I was unable to assign the shortcut. As soon as I pressed the hotkey, I was kicked off into a virtual terminal.
The fix is a KDE solution and is very similar to the Gnome/Ubuntu one linked above. Click the K-Menu and type key (or keyboard) in the "Search" box at the top. (You can also do this by pressing ALT + F2 and then typing "key" in the resulting drop-down at the top of the screen.) The first result ought to just be Keyboard ("Keyboard settings"). Open it. This should bring up the "Keyboard KDE Control module".
Now, click the Advanced Tab at the top. Check the box that says Configure keyboard options and in the list below, expand the section titled Miscellaneous compatibility options. In the expanded list, check the box next to Special keys (Ctrl + Alt + key) handled in a server. Click on OK at the bottom.
That's it. Now the CTRL + ALT + Fn Key will no longer work. I'm guessing that other combinations of CTRL + ALT + Some Key will also cease to work. But that's OK with me.
Hope this helps!