Last modified: 2014-03-22 22:37:11 UTC
Example URL is a diff between [[d:Q2415852]] and [[d:WD:RFD]], which throws a "[6ff49246] 2013-06-25 23:49:04: Fatal exception of type MWException". Using [[d:Special:ComparePages]] (https://www.wikidata.org/wiki/Special:ComparePages?page1=Q1&rev1=&page2=User%3ALegoktm&rev2=&action=&diffonly=&unhide=), gives the "Wikimedia Foundation Error" screen with: " PHP fatal error in /usr/local/apache/common-local/php-1.22wmf8/extensions/Wikibase/repo/includes/EntityContentDiffView.php line 136: Call to undefined method WikitextContent::getEntity() " Neither of these two situations should result in fatal errors, just a message saying something like "You cannot diff between these two pages since they use different contentmodels."
Sounds like a problem in Wikibase extension, because EntityContentDiffView.php is part of that.