Normally holding down k and tapping j or l acts as do the right or left arrow keys – they just step to the next frame or previous frame. Well, when I hold down k, and tap j or l to step backward or forward, it ignores the fact the I'm holding down k. So it just plays, or rewinds. The arrow keys are still working properly.
I've reset FCP prefs, restarted, set default keyboard layouts and looked into the keyboard shortcuts in System Prefs. All of our other machines (10 machines) are having no problems.