[GAMEPLAY] Rengar 5 Stack Ferocity on Bola Strike Bug

http://imgur.com/pFsHjrh?noredirect http://imgur.com/I1m8Moo?noredirect

This has been happening to me for a couple patches now and i havn't seen anyone else post anything about it. It isn't extremely common but it happens at least once or twice a game and in the screenshots i was able to recreate the bug twice in around a minute in a custom game. This bug happens if you have 4 Ferocity stacks and use your E to get your 5th Ferocity stack which causes Rengar's empowered E to go on cooldown which has cost me quite a bit of ganks. T^T