This issue has plagued us for almost a year: Internal Server Error; enable debugging provides no additional information.
Amazingly, if a page includes four or five dashes to act as a thematic change or logical topic break, then the server will shit all over itself. It will also fail to report errors in any of the logs, including error_log and php_errors.log:
text preceding logical break... ----- text following logical break...
I almost could not believe it... But here's the proof for us: Difference between revisions of "SVN". Once we removed the horizontal dashes, the page was submitted successfully. And we were able to repeat the results on other problematic pages. Absolutely amazing...
This damn bug reporter keeps erasing the information we are trying to provide. The problematic version of MediaWiki is 1.26.4. The problem was also present in 1.25.1. MW is running on CentOS 7.2 with PHP version is 5.4.16 and Apache version is 2.4.6.