Hi Brook,
Thanks for your help. Good call on validating the html — I was able to find where the extra </div> tag was being pulled in. I had modified the general.php file to prevent the recurring events tooltip showing (the information in those tooltips is a bit too technical for visitors IMO 🙂 and had neglected to comment out one of the closing div tags.
I fixed that, and now the pages render properly. Thanks again for your help — chalk this one up to user error.