The culprit is xbinkeys, a software made to create custom shortcuts. The CTRL+F lauching xterm is an example in the configuration file (~.xbindkeysrc). Since Ubuntu 11.10 doesn't realise it is an example and use it by default, overriding all other uses of CTRL+F.

In order to set things back to normal do as follow :

1. Open your home folder, and press CTRL+H to show hidden files.


2. Open the file .xbindkeysrc (with gedit).


3. Add a pound (#) at the beginning of each line starting with "xterm" and the following one (most probably lines 46-47 and 50-51).


4. Save and exit.


5. Then either logout/login again or restart xbindkeys: killall -HUP xbindkeys