I think there might be two issues here, one is the lag and /follow bug (which I think I've got a couple of times only) and the other is the way modifier keys interact with movement in wow.

I've had runaway issues with keyclone, but also fairly frequently when I'm solo and not running keyclone (obviously, because what would be the point :P). What happens is (for example) I'm moving and trying to cast a spell with a modifier (or trying to chat), if I'm holding shift down and release the movement key wow doesn't realise that I actually want to stop moving (it gets w down to start moving, but then shift-w up so it doesn't stop moving). Similarly pressing two keys (or a key and a mouse button in my case) which are bound to the same movement direction will result in your character standing still.

I think the only solution is to either be more careful with modifier buttons (says the person who does this at least once a week) and/or to hold down the modifier key and whichever movement button didn't turn off properly.