CMS Made Simple Forums

I am using a template which works fine normally in IE10, 11 but is broken when it is used as a page not found. This works fine in every other browser I have tried apart from IE10 and IE11

This works

http://www.c-h-w.com/privacy/

this doesn't

http://www.c-h-w.com/blahblah/

Now of course a 404 page works differently from a "standard" web page and I have tried using a simple template and it is ok. I was just wondering if anyone else was having a similar problem.

Seems to work here:

I just tried again and on first load it is broken but if I duplicate in a new tab it works which is even odder. If I then reload that tab it breaks again. Doh...