Steps to reproduce the issue

• Create an article containing an "intro text" and "full text" (i.e: it must have a "readmore" break)
• In the intro text put {loadposition test}
• Set "Access" for Registered users
• Create a custom HTML module with just <h1>Hello!</h1>
• assign it to custom position test for all pages
• Create two menu items:
• A "Category Blog" menu item for the category containing the above article
• A "Single Article" menu item, for the above article.

IMPORTANT :

• have the Show Unauthorized links option in effect (set it at the global, component, level, to make things easier and check that it is not overriden by settings at the article and menu items level)

Try accessing the two menu items (the "Blog" and the "Single article") while not being logged in.

Expected result

The custom HTML module should be displayed, in both views

Actual result

The custom HTML module is displayed only in the "Category Blog" view, while in the "Single article" view you'll see the {loadposition test} tag, verbatim.

System information (as much as possible)

Joomla 3.5.0, Protostar

Additional comments

The confirmed (unless expected) issue is that in "Single article" view, when an article is partially displayed (intro text only) as a consequence of it being declared for "Registered" users, the user being "Guest" and the "Show unuathorized links" option being in effect, then the "intro text" is displayed "raw", with that meaning that certain content plugins (e.g.: those based on the "onContentPrepare" event) are not applied to the intro text.

This is a continuation of #9746 (it was started for a different purpose and thus was littered with too many non relevant comments)