Global rename reads the attachment method (original home wiki, merged, autocreated etc) of each local account, then unattaches those accounts (thus erasing the status), and fires a "recursive" job that renames and reattaches one wiki, then creates a new version of itself for the next wiki. The original attachment method is passed along as an array of wiki => method from job to job.
This means that any job error causes the attachment method of the remaining wikis to be irretrievably lost, and the remaining wikis are listed as unattached. (They are not technically unattached, so nothing breaks, but it makes the UI confusing.) fixStuckGlobalRename.php tries to fix this by manually passing in a fake method but only does that for the one wiki it's called on so it doesn't really help. Besides, it's still a fake method.
As a quick fix, fixStuckGlobalRename.php should pass the fake method for all wikis. As a proper fix, the method should be stored somewhere safer (the renameuser_status table seems like a logical place). We should probably fix the incorrect "unattached" records for past renames, too.