Not exactly my problem, but a friendly reminder that it but might be your problem if your site is found here:
http://www.bing.com/search?q="Compatible+UI+Version(s)"+"checked out to"+site:<YOURSITEURLHERE>
Activate ViewFormPagesLockdown feature as instructed here in MSDN.
If you’re using Publishing Portal site template, this feature is already activated, but for other templates you need to enable it manually.
The MSDN article contains also other suggestions for public facing anonymous SharePoint sites that you might want to follow.