It doesn't though. Doing /prat channelnames guild set g (with a space after the g), it just ignores the space, doing set "g " it literally sets it to that, with the quotes.
I also have problems with this. Strangely enough I was able to achieve the "spaced" effect by using the text box on the FuBar module's menu, though.
It's a small detail but I hope this functionality doesn't change. To me, it adds a degree of neatness to the chat window. :)