Thanks! You are correct. Sorry about that - we should have spotted it because it causes pages to fail the HTML validator.
I have fixed this in the official code - and also fixed 2 other validation errors (which may not have been doing any harm, but you never know). Now the page validates fully.
Bug is CONTRIB-1370
and fixed ouwiki version is 2009062200.
By the way - thanks to Helen for passing this on to me! I'm afraid I am not subscribed to this forum because most of the discussion is not related to OU wiki, so it would really help if you could report ouwiki problems using the tracker. If you select 'contributed code' to start with, and then 'Module: OU wiki' in the component field, it will go straight to me. (Of course I welcome forum discussions as well, you can link these in the bug if you want me to read them!)
(If there's something that isn't a bug but just a discussion about ouwiki that you'd like me involved in, um, let me know!)