Maybe, but it's a behaviour that shouldn't be possible to happen. If I have a personal account it's my account, and should be considered distinct from the accou

Maybe, but it's a behaviour that shouldn't be possible to happen. If I have a personal account it's my account, and should be considered distinct from the account of a school/organization, there shouldn't be the possibility that joining one of them will limit what my account could do. That is a personal account shouldn't even be possibly converted into an AzureAD one: if you want it's another account, with another email and another password. This possibility of mistake should never happen.