This issue is reported in following Japanese forum.
https://groups.google.com/forum/#!topic/redmine-users-ja/wb78I8uVJEY
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I'm sorry, attachment:"patch.diff" breaks Redmine rake test.
It breaks activity view items.
Please reject the patch.
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I think this problem only affects the atom of issues list.
There are **updated** tags created by **issue.event_datetime**.
But **issue.event_datetime** is **created_on**.
I think you need to use **updated_on** for the atom of issue list.

I re-create the patches for this issue.
In the first pattern, **issue_controller** overwrites **issue.event_datetime** between atom exports.
The second pattern, **application_controller.rb** and **common/feed.atom.builder**, adds the code for the problem list atom.

Both work, but I don't think it's clean code.
I'll attach both patches in the hope that it will help you think about better code.
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