Cast on Effect with 2 weapon sets. How should it work?

Hello, exiles!

So, we have an ability to appoint skills and passive for exact weapon set.

And we have Cast on Effect, such as Cast on Ignite, or Cast on Freeze.

While basic skills, such as Ice Nova or Firestorm works perfect with weapon sets - Cast on Effect works pretty strange.

Example Steps:
1) Set up Cast on Ignite(CoI) with Comet in it.
2) Open CoI and menu, and set Comet "Used with weapon set: II"
3) As soon as you click on 2nd weapon set - CoI will turn off on main set weapon.

So, in order to use invoked spell - you should set CoI for weapon set 1.

But, what if a player wants to use different type of magic, like Comet, or Orb of Storms, and 2nd weapon respectively?

If will leave CoI just for a 2nd weapon set (for example with Frost weapon and Comet in it) - it will never stack with your main Fire weapon set.

Is it works like intended?
Or am i doing something very wrong?

As for me, logically, you stack up your CoI to invoke some other spells with other weapon set.