Spark bug

Hello
I got a bug with spark when i cast it repeatdly.
At first everything work fine i throw 11 projectiles but after some cast i throw only 3 sparks per cast.
I tried to get less cast speed and i could cast more spark before the bug.
I tried also to get a low level spark with less projectile and i could also cast more time before the bug.
The bug is not only visual my dps on monster is way worse when the bug occur.
My obvious guess is too much projectile on screen and the game dont like it.