Alright, I've just reproduced same error, so now we know when exactly this happen.
Dancso wrote:
I'd like to make a few suggestions. Make the stronger weapons only available later in game. It's very misleading to new players (it kind of was, for me) they might get annoyed by the quick drain. Common sense tells them to use the most powerful weapon.
Weapon/mana behavior is exactly similar throughout the KA. Also, there's a wiki documentation and the manual for the new players

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Dancso wrote:
About experience draining over time. I have two suggestions: 1. Make it unable to lose levels. You "worked hard" for it, a 2 minute toilet break might break your heart.
Umm... is pause not working ?
Dancso wrote:
Also make the drain stop during cooldown (at the end of each wave, when counting down to next wave) since there is nothing to kill, there should be no penalty.
That's an interesting suggestion, we may think about this.
Dancso wrote:
I have a question too. Does experience scale with the enemies' health? I noticed the health modifier on server settings, do healthier monsters give more like the modifier in kmod?
Yes, more health monster has, more experience you get from killing it.
Know, though, that when your character reachs higher levels he gains
less experience for each kill. On low levels, however, if you kill something really powerful, like Minotaur or Heresiarch, you may get several levels at once. Same counts for fragging opponents in other game modes.