Thread:Project:Support desk/Section is not saved after concurrent editing

Hi! Using MediaWiki 1.20, PHP 5.3.5, MySQL 5.5.9 in Windows 7. I have installed diff3 and declared it in LocalSettings.php 2 users start editing different sections of a single page at the same time. User A edits section A and saves the page. But when user B edits section B and saves the page, the modifications of section A gets lost! Why is that happening? I thought that MediaWiki could handle concurrent editing of different sections.