I had the same problem. Turns out it was an execution window that was buried. It doesn't show as an "open window" when you look at the taskbar at the SSMS icon, so it's deceptive. ALT-TAB your way through the windows and you should find it.
The open windows was:
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…