WASD + Warpath intermittently fails to proc Void Well

Using WASD + RMB, will have 3 void essences but Warpath will proc void essence to refill mana to 30% but restart Warpath. No, the mana cost hasn’t climbed high enough to immediately go to zero again; bug does NOT occur on normal M+KB control, bug also does not occur if I change Warpath to Spacebar. Just when I use a mouse button + WASD.