Casting/Canceling spells with left/right click BUGGED

A spell I'd like you to use as an example while reading my explanation. - Morgana's Q - Dark Binding

I've never had this issue before, I used to do this a lot whenever I changed my mind; whether I wanted to cast my spell or cancel it. Before, I used to hold my spells by holding my left click ... if I decided NOT to let go (cast) of my spell, I'd just right click my mouse while still holding left, and then the spell would be canceled.

Now it seems different, whenever I decided to NOT let go (right click) of my "on hold" spell, the spell wouldn't be cancelled, but instead! it will let go of it self (it's like I casted the spell with left click WHICH I didn't and never planned to cast it)

Clarification [just in case you guys are getting confused with the clicks I'm talking about] Left Click - to cast a spell Right Click - to move from place to another On Hold Left Click - about to cast a spell but you're holding it for right timing Right Click while Left click is on hold - to NOT let go of the spell (cancel it) <--- this is the problem, this no longer functions, now it just lets go of the spell

Reading this seems like it doesn't make sense, but hey! I tried my best to explain my issue.