To reproduce:

1. Create a reference with an email (e.g via the travel demo contact form)
2. Confirm consent trough the confirmation email or via the visitors app.
3. Remove consent for email via visitors app.
4. Check reference: email property is deleted.
5. Create a new consent group, e.g. config:visitor-manager/config/personal-fields/details/message=message
6. Go to the contact form, now it should require consent for the details group.
7. Confirm consent.
8. Remove consent for the details group.
9. Check the reference, the message property is not deleted.