Yes, this is was bug in the original 1.3 beta 1 release. It occurred if you added a navigation link to a page which is provided by a plugin. If you downloaded 1.3 beta 1 within the first few hours, you can fix it by modifying this line in qa-page-home.php:
if (isset($categoryslug) && isset($custompage)) {
... to ...
if (isset($categoryslug) && isset($custompage) && (!($custompage['flags']&QA_PAGE_FLAGS_EXTERNAL))) {
Since this was caught so quickly, I've replaced the current 1.3 beta 1 download with a fixed version.