I may have found the problem. PHP "Bug"

http://communityseo.com/forums/Fix-for-random-blank-pages-t3076.html

I'll quote it here for future folks doing searches.

Originally Posted by communityseo.com
It has been seen on some recent PHP versions that some random pages will just output blank html. In troubleshooting, the entire PHP page load is executing - just no HTML is being output.

This is a PHP "bug" (which the PHP team doesn't classify as a bug...) and can only be fixed by editing the php.ini file. You may need to ask your host to perform this edit for you if you don't have access to the php.ini file (i.e. if you have a shared hosting plan).

Open php.ini and add at the end of the file


CODE
pcre.backtrack_limit = 9999999999
pcre.recursion_limit = 9999999999


Save the php.ini file and restart Apache. Verify if the blank pages are now loading correctly.