Yes we did change thieving formula, your chances of succeeding are more balanced and capped at 85% max. With new formula you have about 80% chance to thieve a hero at 99 thieving, so it is 5% less than before. If you barely meet thieving requirements you have around 60% chance of succeeding, and with every level you gain you have additional 1%.

Why was thieving nerfed? This is completely unfair for those who have gained 99 thieving and gotten masks from the summer event in quick succession. And why not announce the nerf? Will it be for the event time only?

Ok correct me if im wrong if the chance to succede on a hero is about 80% at 99 and 85% is the cap, the cape will only serve about a 5% bonus instead of what  the 20% chance it's supposed to?

Thieving cape makes you 20% less likely to fail any given pickpocket attempt . This is how i think and always thought thiveving cape works .  Let's say it's 20% chance to fail at heros , with the thieving cape u would fail 16%.