This bug has been reported already over the years, but figured I’d add another report.
While playing Rexxar, it is possible to cancel your W and still receiving full cooldown+mana costs. I believe this is triggered by spamming D commands while also throwing a W out, causing Misha to move and cancel her W.
(Some previous reports of this bug:
This bug is, surprisingly, still in the game as of today but it seems like there has been a poor attempt at fixing it since now there seems to be a chance for the normal (above explained) bug happening and, other times, you will just press the button, nothing will happen but you wont lose the cd either (cant say about the mana though).
hello,
I would like to report the same bug with the W (Misha’s stun) in my last games with Rexxar.
Two times in a row in the same game i pressed W, nothing happens and i lost my CD. And today again this bug. Quite of frustrating coz without his stun, Rexxar is really week (and almost useless). And this bug is here from many years now… Could be nice to do something to fix it 
Bump
We should re open every other bug report topic from the last 9 months if this has come to their attention JUST NOW.