This sounds like a fairly harmless issue and it should be easy to fix, so I'm leaving it for some new developer to look at :)
Change 365170 had a related patch set uploaded (by Eugene233; owner: Eugene233):
[mediawiki/core@master] Page move with same title shows generic error
I think I might be able to submit a fix for this today :)
Change 365170 merged by jenkins-bot:
[mediawiki/core@master] Improve "selfmove" message's wording
Thanks @Eugene233 for working on this & @Legoktm for merging :).