Fizz "E" Grayed Out and Unable to Cast Bug

When playing Fizz, his "E" ability grayed out at random times and was unavailable to be cast. The ability would temporarily come back for a random amount of time, once after killing an enemy champion, and another time after using a full ability combo.

Uncertain how to recreate the bug since there is no detectable correlation between in game actions and the bug occurring.

Reported after 1 game since it is not a bug that can be recreated.

Video: http://plays.tv/video/5762deefe5a478c5ce/fizz-e-bug-wtf?from=user