After installing Scribunto, several users have reported problems with text/plain and have been using the fix at the end of this blog post: http://trog.qgl.org/20110815/setting-up-infobox-templates-in-mediawiki
The XML file that is output in step 3 appears to erroneously (?) use text/plain as the format type. If you edit this XML file in your text editor and replace all incidents of ‘text/plain’ with ‘CONTENT_FORMAT_TEXT’ (I only found two), the import will be successful and the infobox tags looks like they work.
Version: REL1_21-branch
Severity: normal