Don't let the first debuffs you apply be temporary!
If you apply 6 blindness for 5 seconds but those get reflected, you (of course) take 6 blindness, but then after 5s you cleanse 6 blindness from your opponent!
@fucifer, this doesn't feel like a bug per say, but in other games I've seen where it works like this, the debuff is usually applied along side a "remove blindness" buff rather than having the sword acting again in 5s. That makes the interaction when you first encounter it less surprising (though also it makes it possible to steal the buff which maybe you didn't want to happen?)