>Is this something that can be stopped?

Yes, in next version of Fox :).

The chr(19) (aka ctrl+S) happens when you save a saved prg file again. Fox doesn't do anything if the file wasn't changed since the last save, so the menu bar is inactive, and chr(19) isn't acted upon, so it gets into the text. That makes the text changed, so if you delete the character, next press on ctrl+s now works.

Same goes for chr(23) (ctrl+W) in the command window - the close+save has nothing to do there, the command window is saved on quit automatically, and there's no way to save+close it before that, so ctrl+w is not caught there at all, and the chr(23) is taken literally and stays where you typed it.