justpi: thank you so very much. I was really beginning to tear my hair out, as I couldn't find anything wrong wiht my content, and I don't tend to copy and paste from Word.
I was not looking at the comments, just my post. Removing the
<li> tag from the last comment worked did the trick.
In answer to your question "what was I trying to do by adding those tags?", I should perhaps make the point for others reading this in the future, that as a content creator I had done nothing wrong.
I did not add the tags. The tags were part of a comment made by a reader, and i guess that this effectively means that any time a comment is made on a WordPress blog by a third party, there is a chance that comment might inadvertently include code that screws up the layout.
Not sure that's great news, but seems to be how it is. I guess I'll just have to keep an eye on comments, however I'm not sure that I get to see the actual code when a comment appears for moderation.
Thank you once again very much for taking the time to help me figure this out : )