Are these new listing's or existing that you are revising?
The   is a space, the other thing that I do is when I paste into Auctiva I select all in html and delete it then I paste it in standard mode from notepad.
I have seen this when I get lazy and paste from old listings but not once I have posted a clean listing.
I will pay more attention to this to see if I can nail this down as I have only seen it in a few listings of mine.
Have you put in a support ticket?