I think this is a bug.
When editing a user, some TLDs are not being validated correctly. Tested domains .pt and .edu render the error "Enter a valid email address". TLDs like .com validates OK.
Email is not valid for some TLDs
I don’t think this is a bug, this is typically due to having DNS issues. You can disable the setting Verify Email Addresses under Admin Panel > Emails > Settings.
Cheers.