"KEEP VERT" and "Kill H/S" have issues with "hover" like crafts.
Build a craft with one ore more jet engines faced down and a Mk1/MK2 cockpit horizontally (like a normal plane).
Kill H/S will work perfectly but keep vert will think the craft is in a 90rot and because of the combination will start flying in a 45 degree angle.
Adding a upward facing mechjeb2.0 party and switch to "Control from here' on it will fix the "Keep vert" issue but the Kill H/S will start to become highly unreliable.