Asura Aura not 100% with SD/MPC set

I'll post my MP Cost/SD/ID/Tankish set:

Purity Claw II+9 Kagan QC 1
Red Bringer+9 Rossam MP Cost 2
Taenia Beret Up+9 Rossam QC 1
Accesory QC 1
Chief God's Stone Rossam (I'll put QC 1)
+ Sauro II Al

With this set I have -100% Mp Cost, Lowest ASPD, I can Spam Rush, Asura Aura has like 2 seconds SD, I can spam item usage, plus I have 80%+ Melee Resist.
It's pretty good.

*Asura Aura recovers it's percentage based on the percentage of MP Cost when you use it before it reaches 0%.
So if it is at 1% and you use a -100% Mp Cost Set it will only recover 1% of your Asura Aura, ending being 2%.

So you'll have to lower it's percentage to 0% and then use it again, or use Asura Aura without negative MP Cost.
It's completely normal.