Another lovely one, for ages (probably still) OneDrive would purge it's local copy whenever you turned it off or uninstalled it. That was probably one of the most frustrating things that Windows has ever done to me.
Edit: Lord, can we please talk about "3D Objects" too? Who the hell got promoted for shoving that down everyone's throat in half a dozen places? Every week I get an update I have to run a regedit script to remove all the bullshit they've shoved into Explorer for absolutely no reason.