As always with Windows, though, the UX isn't quite right... If that spot is occupied by a pinned shortcut, Windows will run that program. But it won't remember

As always with Windows, though, the UX isn't quite right... If that spot is occupied by a pinned shortcut, Windows will run that program. But it won't remember that it's done that - so if it takes a while to start, and you press the key again, it will see there's a shortcut to a program that's not yet running, and... run the program again. So while trying this feature out, and wondering why nothing was happening, I managed to open 3 copies of Unity and 7 copies of Visual Studio.