Krinkle reported a blank page returned by http://commons.wikimedia.org/wiki/Category:No_Wikisource_book_djvu?action=purge
Web inspector shows that this was a 500 Internal server error.
Werdna suspects this was a direct cause off
Mar 14 00:13:30 10.0.2.169 apache2: PHP Fatal error: Allowed memory size of 83886080 bytes exhausted (tried to allocate 961189 bytes) in /usr/local/apache/common-local/wmf-deployment/includes/memcached-client.php on line 951
The category has 630 items (according to PAGESINCATEGORY. and contains some very big files (some 50+ MB files among them)