Multiple tags in URL broken in 6.8

[frogsplash]

Hi gang, thanks for all the work y'all do. I've been a WordPress user for a looooong time, really appreciate the community's efforts over the years.

There's a new "bug" that got introduced into 6.8, and it's unfortunately broken a lot of my websites. (I say "bug", but maybe there was a reason this change was made.)

Short and sweet: the ability to filter tags via the URL has been incredibly useful. I run many asset library type websites, and being able to display certain posts by their tags is essential.

Example:

​https://bagofhurt.com/tag/2025+test-tag-1/

In this example, this page lists all posts that have both of these two tags. All good so far. The kicker comes when you flip the tags:

​https://bagofhurt.com/tag/test-tag-1+2025/

While you get the same post result, the listed tag in the H1 still says "2025."

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To contrast, here's the same page in WP 6.7.2:

​https://bagofhurt.com/old/tag/test-tag-1+2025/

The tag listed first in the query has always been used for the H1 display – until 6.8. It looks like it now uses the first tag alphabetically, regardless of the order.

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I don't know the WP codebase well enough to tell someone where to look, but if this an easy fix, I would greatly appreciate a patch. Or if there's a better way for me to replicate the behavior I'm after?

It looks like this thread might be related: https://core.trac.wordpress.org/ticket/63255

[websiteredev]

Reproduction Report

This report validates that the issue can be reproduced.

Environment

• OS: Windows 10 Build 19045
• Web Server: Nginx
• PHP: 8.2.27
• WordPress: 6.8.1
• Browser: Chrome Version 137
• Theme: Twenty Twenty-Five
• Active Plugins:
  • None - Fresh Install

Actual Results

• ✅ Error condition occurs (reproduced).

Steps

1. Created new site on WP 6.8.1
2. Added tags "test1" and "abababa" to Hello world! post
3. Navigate to /tag/test1+abababa/
4. H1 shows as "Tag: abababa" with Hello world! post listed
5. Navigate to /tag/abababa+test1/
6. H1 shows as shows "Tag: abababa" with Hello world! post listed

[websiteredev]

Patch Test Report

This report validates that the indicated patch addresses the issue.

Patch tested: ​https://github.com/WordPress/wordpress-develop/pull/9201

Environment

• OS: Windows 10 Build 19045
• Web Server: PHP.wasm
• PHP: 7.4.31
• WordPress: WordPress 6.9-alpha-20250706.084457
• Browser: Chrome Version 137
• Theme: Twenty Twenty-Five
• Active Plugins:
  • None - Fresh Install

Steps

1. Create new site using WP Playground link from PR #9201
2. Added tags "test1" and "abababa" to Hello world! post
3. Navigate to /tag/test1+abababa/
4. H1 shows as "Tag: test1" with Hello world! post listed
5. Navigate to /tag/abababa+test1/
6. H1 shows as "Tag: abababa" with Hello world! post listed

Actual Results

• ✅ Issue resolved with patch.