If you search the forums and Internet, you will notice some Blogs have problems with feeds. I know this is a random problem, but its annoying. The post below explains how to solve it by adding a small piece of code. As far as I understood, the code just eliminates blank characters from the beginning of the feed. I think (it has to be tested), this piece of code is harmless for the feeds without problems. I suggest adding it to the future releases. The post says something about the comments feeds as well, my comment feed has not the problem character because I use pretty URLS.
I wrote about that in Portuguese in this post.