The FieldId elements defining the columns in question were missing two attributes: RichText="TRUE" and RichTextMode="FullHtml". New sites based on this template are now working correctly but MS has recommended we not change the site template for the sake of existing sites. We're therefore exporting content, recreating the site, and importing content back in--a hassle but should do the trick.
DisplayName="Publishing Page Content Bottom"
The MSDN documentation currently reflects this structure but I'm not positive it did previously... our mistake either way but at least it's fixed now and the doco is accurate.