Angelo
may be you've unintentionally assigned "k" to some menu item. (It's just a matter of pressing a "key" while focusing the item with the mouse pointer).
Bob Marcan
Shouldn't the same behavior will be in all the other applications?
If you've accident set a hotkey in claws-mail, it'll only apply to that application. And most likely, only when that application's window is active.
I've set hotkeys in (another application - OBS studio), and it meant you could use that key when typing in it. It would have nice to hit the space bar, for example, to switch between cameras. But doing so meant you could use the space bar to type a space in its text editors.