No Text in Explain?
With Simple URLs and vBulletin's debug mode enabled, you will get a "There is no text in this page" if you click on the link at the bottom of the page that shows you the database explain.
This is caused by vBulletin thinking that no query portion of the URL exists yet, and adds the question mark to the URL before appending explain=1. Unfortunately, if they had checked for $_GET values, rather than the appearance of a ?, then it would have been correct.
Workaround in the next build, but Jelsoft should be the ones to address this issue.