Affects Version/s: 4.2.8
Fix Version/s: 4.4.0
I tested this in event registration with the demo site. It may be true other profile uses such as 'create mode' or Contribution pages as well.
1. Create a profile that contains names, emails, address, phone, "current employer", "birth date", and a custom data individual field such as "marital status". Make ONLY name and email required.
2. Create a contact and populate the data listed above
3. Register for an event "as another person" using the profile you created in #1.
4. Register in such a way that your data entry matches the existing contact (i.e. emails match, and de-dupe rule is email). Fill out ONLY name and email. The rest is blank
5. Observe that name and email are preserved upon submit. Address and phone are preserved. "current employer" the relationship is destroyed. Birth date is erased. Custom individual data like "martial status" is erased.
Users could forget to enter data on a public profile optional field, this doesn't mean we should delete existing data. Data should not be overwritten with null values. Blank current employer should preserve existing employee relationships, not delete them.