I have a custom field type Email Address set to required. The form will submit even if the field doesn't contain an email address. If I do a check using cred's form validation hook and the wordpress function is_email, the form behaves correctly and doesn't submit if the field doesn't contain an email address.
Thanks for testing. I haven't changed anything regarding the field settings (they've always been "required" and set to validate as an email) however on checking them, the "validate as email" box is currently unchecked which explains why it's not validating (!) but not how it became unchecked. I'll monitor in case it happens again.