So I’ve been working on a custom map, and placing lots of props to make it look nice. I’m zoomed in messing around with a prop, when suddenly it selects every prop on the map. Moving the mouse moves every single prop together. I panic, and instinctively press right click, which is usually “cancel” when things are selected.
Suddenly, every single prop on the map is gone. All of the work, poof, with no way to get it back. It’s happened twice while working on the map so far 
So, either there needs to be an undo button, right click needs to not be delete, or the bug where every prop gets selected and stuck to the mouse needs to be fixed.
Oh well, time to try again!
(It has something to do with the “A” key I think)