Trying to insert a wikitable when editing a page via a Form doesn't work. On saving the following error is shown:
"|" is not allowed, except within {{...}} or [[...]]

Product Version
MediaWiki 1.28.0
PHP 5.5.9-1ubuntu4.20 (apache2handler)
MySQL 5.5.53-0ubuntu0.14.04.1
PageForms 4.0.2 (f0816ba) 22:12, 6 January 2017