Yeah poison and disease is weird in that it has spell components that do some funny things. The counter is an internal register for the debuff that when you remove them all, the debuff is completely lost, but taking off portions of it doesn't make the dot have any less strength
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It's also one of the reasons when you put poisons and diseases on other mobs they carry such a high aggro
[You must be logged in to view images. Log in or Register.] The counter spell component counts as its own debuff on aggro table