You can usually use ctrl-z to undo. As long as the edit box is still open, that is.
In other news, I finally managed to get rid of my nbsp bug. This is one of these bugs that are so exotic you cannot even suspect that it is this kind of bug. I reinstalled the Lato font. Imagine this, the automatically installed font that my OS manages, somehow was missing the character for nbsp. Or it had 0 width. If I had manully installed those fonts, I would not be that surprised. But I never touched system fonts.