can't remove shortcut

I'm trying to remove a shortcut without success (so it can use it for something else)

eg. if i remove Ctrl + I from the KeyBoard Shortcut menu, it is still active when I use the command, in this case it still inserts source text into target segment. Even after I open and close the software. Seems to be the same problem with other cntrl combos.

Is there something else I need to do ?