Just before reading this. I APOLOGISE IF THIS BUG HAS ALREADY BEEN REPORTED! I COULDN'T FIND ANYTHING SIMILAR TO THIS! THANK YOU FOR UNDERSTANDING!
So, I just started a new world in the latest snapshot 17w18b and I started mining cobblestone with a wood pickaxe. I was using it until it broke. When it broke it said I got the advancement "Serious Dedication". It's not so big of a bug, but still..
Thank you for reading!