What build did you upgrade to and where were you coming from? When I upgraded to 10522 to 10414, I had some weirdness with my bitmap fonts. It wasn't quite as dramatic as yours--there was an extra pixel between characters. Opening the font in Stencyl, making some kind of edit so that the font was marked as 'needed to be saved' (asterisk on the tab) and closing it fixed the issue. I suppose that forced a re-save, which corrected the problem.