Au contraire, the error is in http://abovethecastle.wordpress.com/2013/03/20/dreadlocks/ and it is most assuredly an HTML error. Whether or not you mean to use HTML code, everything on the web is in HTML, so if you copy-paste anything from anywhere in the web you are adding HTML you can’t even see. If you paste from Microsoft Word you’re doing the same, as it adds all kinds of junk code.
Make sure you have selected “WordPress should correct invalidly nested XHTML” and saved that setting. Then edit that post and Update and see what happens.
The error is in that post, but there’s no HTML error in the sourcecode of the post. The problem is that the spaces between the words aren’t regular spaces: the editor doesn’t recognize them, so the lines don’t break where appropriate. Try this: copy all the text from your actual blog page, then edit the post, switch the editor to Text, select all, paste; then switch to Visual, turn the headings back to bold, click Update.