This bug is almost certainly the same as the wizard attack slow from overheat not being removed when you vent.
-build: waystalker moonfire with kurnous reward (energy restored on kill)
-attack so you have no energy
-ult and restore energy
-attempt to attack. You have the energy you still can not attack (possibly til you restore enough energy the normal tick way to take you to where the threshold would be without the ult)