Gameplay bug with akali and lux

I had problems while playing akali... When I fight a lux... when lux would use FINAL SPARK on me as akali, I can use TWILIGHT SHROUD right before I get hit with FINAL SPARK and it would cancel out the lux ult as if it didn't hit akali... I found out that it wasn't just a one time thing cause it kept happening over and over. Also TWILIGHT SHROUD can be used to Dodge many other champion abilities. I felt bad that the lux couldn't hit me and other champions other wise I would of died in those games a million times. Hope this helps :D also this is my first bug report (tell me if you need any more info)