I can’t believe it took me this long to discover this solution, and by accident as I stumbled on a Joomla community forum post…

Even if you turn off the WYSIWYG editor, Joomla breaks some custom HTML code in articles / content items. According to this post, following these steps will allow you to use custom HTML — “Edit HTML Source” — without having the system break your custom coding.

  • Goto the Article Manager.
  • Select “Parameters” (the button on the top right).
  • Under Filtering options, choose:
  • Filter groups: select the groups that are allowed to use HTML code, e.g. SuperAdministrator
  • Filter type: Whitelist