So I was originally on Unity 5.5ob3 when this begun happening to me and it's the weirdest thing. When I add new assets to my scene (or so it seems) Unity will take a lot longer than usual to run the scene in the editor and then suddenly, it'll open all of my Windows apps running in the bottom right hidden icon tab along with other apps. I have no idea what's causing it. My feeling is that it tends to happen when I have a lot of assets running in my scene. I'm currently on Windows 7 x64 with Unity Pro and don't know how to debug or get to the bottom of what's causing it.