Bind:
W to forward movement.
S to backward movement.
W+S to toggle combat pace.
S+W to toggle walking.
Now enter the editor with any character. Run forward (or backward) by holding W (or S) and try to toggle combat pace or walking by still holding W (or S) and then pressing the opposite movement button S (or W).
Your character will now stop, then continue moving at the new movement speed.
The awkward, short pause your character makes is the issue.