Sion Q and R ability bug

I have been playing a lot of Sion lately and noticed that if you mid charging Q or R and get interrupted, you no longer are able to cast the ability? For example, I was playing Sion against a Wukong and Jarvin IV, I would start charging my Q for the knock-up stun, then Wukong uses his ult and knocks me up...After wards I was no longer able to cast Q or R, Same issue if J4 would flag and drag knock me up....Please take the time to look into this!