Many RSS readers use the description field in a feed as a surrogate when there is no title, displaying the first 'X' number of characters from the content. This is expected behaviour but they should really support title-less posts properly.
(It's one of the reasons I moved to Feedbin.)
It's been pointed out on a couple of occasions that various feed readers include HTML tags in the "title" for my title-less posts.
The conversation yesterday lead me to discover that the way WordPress contains the item description in a CDATA wrapper is causing this. A test feed without the CDATA wrapper seems to work okay.
So I need to find a way to modify the feed on the fly or create a custom template. I've had a look and don't think the former option is possible.