Problem i met as essence drain

sorry english is not my first language, I have a few problem

1.Using curse fail sometimes, Mana are deducted but nothing happen. Not Stunned, not getting hit, can fail to cast consecutively 1-5times. And you know casting once cost 70% above mana, This is very lethal please fix this

2.Why Wither not counting as a aura, it didnt receive any buff form aura magnitudes.