[5.4] Tag feed (RSS) shows only intro text, full text after Read More is missing when "Show Intro Text = Hide"

[CSGoat0]

Steps to reproduce the issue

1. Navigate to Content → Articles → Options
2. Under the Articles tab, set Show Intro Text to Hide
3. Under the Integration tab, set Include in Feed to Full Text (or any setting, as this bug affects all)
4. Click Save & Close
5. Create a new article:
   • Title: "Tags RSS Feed Test"
   • In the content area, type "AA" (intro text)
   • Click the Read More toggle (CMS Content → Read More)
   • After the read more break, type "BB" (full text)
   • Assign a tag to the article (e.g., "TestTag")
   • Click Save & Close
6. Create a Tagged Items menu item:
   • Menu Title: "Tag Feed Test"
   • Menu Item Type: Tags → Tagged Items
   • Tags: Select "TestTag"
   • Click Save & Close
7. On the frontend, access the RSS feed for the tag using the URL:
   • http://localhost/tag-feed-test?format=feed&type=rss
   • Or directly: http://localhost/index.php?option=com_tags&view=tag&id=XX&format=feed&type=rss

Version

5.4

Expected result

The feed should show only the content after the Read More break ("BB") because Show Intro Text = Hide.

<description><![CDATA[<p>BB</p>]]></description>

Actual result

The feed shows only the intro text ("AA"). The full text ("BB") is completely missing from the feed.

<description><![CDATA[<p>AA</p>]]></description>

System Information

• Joomla 5.4
• PHP 8.5

Additional Comments

• HTML view (full article): Only BB appears ✅ (correct behavior)
• Category feed (com_content): Shows AA + BB when should show only BB (different bug, already reported separately)
• Featured feed (com_content): Shows AA + BB when should show only BB (different bug, already reported separately)

Comparison of related feed bugs

Component	Bug type	Behavior
com_content (Category/Featured)	Too much content	Shows AA + BB when should show only BB
com_tags (Tag feed)	Missing content	Shows only AA, BB is completely lost