A minor change in Unity 5.4.f1 (from 5.3.whatever that I was using previously) that about got me: Assets under project view now hides the .cs extension on scripts, so if you type DragLaunch.cs, it creates DragLaunch.cs.cs and names the class “DragLaunch.cs”. I thought people learned not to hide filename extensions back in the I Love You virus days when the virus was called ilvoveyou.txt.vbs but showed up as the apparently-safe iloveyou.txt!
