Low ICE DEMON skill bug

Klock is already weak to fire, so casting Ice Demon on it does not alter fire skills' damage against it.

However, casting Fire Demon would indeed render it neutral to fire, reducing the damage of other fire-based skills, which I agree is counterintuitive.
This is something that's done directly from the client, which means that it is intended original behavior. What happens is as Xessuz wrote, the monster is simply rendered neutral to every element except fire (for Ice Demon) or ice (for Fire Demon), that are set as weak.

I'm not against changing that (I don't even know why it was made that way to begin with...), but as it's not a bug, it would be more suitable for a suggestion thread.
Not gonna mark this one as "not a bug" though because, looking a bit into it, it might still not be correctly handled by the server, I'll have to figure it out more once I have extra time.

Do feel free to provide numbers though, yes. Thank you!