Sion's Decimating Smash (Q) blocks you from clicking the mini-map and pinging.

I sometimes play jungle Sion and, when jungling, I have the healthy habit of checking lanes often. Once I click Sion's Q I expect it to charge up to its maximum damage and CC while I'm scouting the lanes. However, Sion will stop charging his Q on left click, including when you click the mini-map. This may seem insignificant but it can be really frustrating sometimes.

This also happens when you try to ping while charging Sion's Q. In a game where 0.5 seconds can make the difference, this is a big deal, as you can't warn your teammates about incoming danger while charging the ability unless you stop casting it early.

My suggestion is having the ability cancel only if you click Q again or if you right click to move, but not when you left click.