Weird merge bugs

So I have a bug that results from another bug, and I'v found neither of them in the issues. First of all, I have imported people and companies both from my mail/calendar and from an excel sheet I use to use as my CRM, so I have some duplicates. When I try to merge them, I have to always give priority to the one with an URL, otherwise I have an error that says that the merging failed, and the merging does not happens but still one of the duplicates will be deleted. So I have to restore it and try to merge the other way around. It usually works, but here I did just that, and things got weird. When I filter my companies by name, I can isolate the two duplicates. If I do the same with an SQL request, it's the same, all good, I can find the two identical companies. But when I click on "merge", I have three companies to merge, 1 and 3 being the same. They are so much the same that firt and third tab are both selected at the same time. And of course I can't merge. I don't know how to fix that because it looks good in the company table, so I can't just modifiy the database and be good with it.