Exceprt function is a WordPress function, and used by the theme, it has nothing to do with GD Star Rating. But this function removes all HTML markup from post, and that also removes big parts of the rating block and you see only pieces of rating data.
Excerpt is added by the theme (most themes use it), and if your posts doesn’t have sepparate excerpt text, it will use content call to get it. If you add excerpts to posts, this problem will not happen.
You can disable GD Star Rating auto insert feature, and add rating blocks manually through the theme, but this is only if you know your way aorund wordpress themes and php.