The plague is back: "Attempt to delete the sole visible or iconified frame" strikes again

I've just hit an old bug that I often saw reported but never experienced myself. I always start Gnus using the toolbar "news" button, which opens up a nice Gnus frame and removes it when you press `q' in Gnus Group buffer. Yesterday I switched to WindowMaker and configured it to automatically place the Gnus frame to a different workspace (I used to do this manually). Since then, `q' signals the "Attempt to delete the sole visible or iconified frame". The same error can be repeated by simply pressing `C-x 5 0' in the frame in another workspace. I remember that Jan did some work with this bug. Jan, I'll provide any data you might need to fix this.