I found a possible bug when developing themes. One of my clients use a theme with a blank in the folder name like this:
Which works fine so far, but each time I try to call up the theme directory uri like with get_stylesheet_directory_uri() I will get it like this:
Not sure if this is a bug. It can be solved easily by renaming the theme folder (like replacing the space with hyphen or underscore), but it took me a while to find out that this was the problem, so maybe it might be helpful to know (or maybe fix it in the next version).