Do you have an AMD? You might try updating your motherboard/cpu drivers. There was a bug in the hardware drivers that would randomly pick a time off either core.

Effulgent, what do you mean by "alt tab out and set the affinity of the program to 1 core"?

i have what seems to be the same issue. i also have an amd cpu. it's just as you described, clicking to move my champion like 'glitches' and jumps them back. it almost seems like it's connection lag, but my connection is just fine.

Also, one thing i noticed is that it only starts happening after a few games of playing. and it seems to build gradually. oddly the way i've been fixing it is restarting my computer, which doesn't make much sense to me. i would think exiting the game would be enough to 'reset' the issue without having to do a full reboot.

i'd love to know of a fix.