Steps to Reproduce
- Create a page, "Foo", http://localhost:8181/wiki/Foo
- Go to the link page form. E.g., http://localhost:8181/wiki/Special:NewItem?site=my_wiki&page=Foo.
- Press "create"
- The page is linked to the item
- Form validation fails for the current wiki's site identifier (and also for others I've tried)
The issue occurs in stock MediaWiki, Vagrant, and Docker development environments: