Engineers and Weapon Switching Effects
I am fairly certain that effect only works with actual weapon switching (default “`”) and not kits. I believe kits are more like bundles right now and seeing as an engineer cannot switch weapons and only kits, this rune is useless in my opinion. Arenanet has said in the beta that there were some mechanics they were going to change pertaining to kits so I am not sure if they will change this in the future.
Hope this helps!