Not being able to cancel abilities

Occasionally when i cast abilities and i hold the button to see range, AoE, etc and delay the casting, i cannot right click to cancel the ability.

This is incredibly infuriating when i hold the R button on an ultimate and this bug occurs, putting my ultimate on cooldown and wasting it.

In addition, when i hold an ability button to see it, the cursor will only move itself in short bursts and i cannot move it fluidly. Very annoying bugs that i hope will be fixed.