GOOD FEED? Okay, I think I understand the problem now. I have, from time to time, been writing out blog entries in a Microsoft Word document and then pasting them into the Blogger "Create New Post" box. Evidently, Microsoft Word (which I've already learned to hate on other grounds) sticks in extra, invisible characters that screw up the RSS Feed. The solution seems to be for me to save the Word document as text-only before transferring to Blogger. I will do this from now on and this post has been done in this way. Please let me know if there are still problems.
Thanks to Greg Gershman and Jim West for sending advice.