Page editnotices displayed outside of the standard edit form resolve magic words like {{PAGENAME}} incorrectly. They refer to the title in the global context, whatever it is, rather than the title of the page.
You can see this problem on MassMessage pages on Meta-Wiki, for example:
- Visit https://meta.wikimedia.org/wiki/User:DannyS712/Mass_message_page_testing
- Click edit → https://meta.wikimedia.org/wiki/Special:EditMassMessageList/User:DannyS712/Mass_message_page_testing
- Note weird link at the top:
This broken editnotice is generated by https://meta.wikimedia.org/w/index.php?title=MediaWiki:Editnotice-2&action=edit when it tries to transclude {{FULLPAGENAME}}/Editnotice, but {{FULLPAGENAME}} actually refers to "Special:EditMassMessageList", so it can't be transcluded.
Similar issue would affect VisualEditor, but there is a "dirty hack" in place to prevent it: https://github.com/wikimedia/mediawiki-extensions-VisualEditor/blob/b94265acc30e546ce4762d4f328002b43c45b3da/includes/ApiVisualEditor.php#L165-L169