Strange bug when using .inc files

Hi, For the site at http://www.room3records.co.uk/nervous/ I'm using .inc files to load in a header and footer, passing a variable to the .inc header so that it can work out which heading to highlight and then using include() to include them. For most pages this is working fine, but on a couple the bar on the left hand side of the content area disappears. I've looked fairly carefully at the HTML generated and can't see the difference between those where it appears and those where it doesn't. I don't think this is a PHP problem (the host is using 3.0.9 IIRC) but want to eliminate all possibilities. Anybody have any ideas? thanks. James.