Why is the old display name shown in person field in SharePoint online?

I accidently misspelled the name of a user in SharePoint online. I corrected it in the portal so that both the surname and the display name is written correctly.

If I search his name in a person Field in a SharePoint custom list, the search result spells the name correctly. But after the form is saved, the old, misspelled display name is used.

Any ideas why this is happening? Both the portal and the user profile list are showing the correct name. I would Guess this was the result of some kind of old name cache, but a week has passed and it is still an issue. Please help!