Google Contacts API "Invalid request." 400 error on name change - google-api

Question

Updating a contact via the Google Contacts API fails when trying to edit a contacts name only without any other changes (besides updated time).
Important note: When the name change is sent along with an email or phone number change it succeeds... only when the name change is sent alone does an error occur. For example changing the contact name and changing 1 character in the email address (or phone number) makes the request successful.
Response from Google Server (http_code 400): "Invalid request."
<entry
xmlns="http://www.w3.org/2005/Atom"
xmlns:gd="http://schemas.google.com/g/2005" gd:etag="*">
<id>http://www.google.com/m8/feeds/contacts/example%40gmail.com/base/realcontactidhere</id>
<category scheme="http://schemas.google.com/g/2005#kind" term="http://schemas.google.com/contact/2008#contact"/>
<title>SameFirst DifferentLast</title>
<updated>2019-04-22T18:55:59+00:00</updated>
<gd:name>
<gd:givenName>SameFirst</gd:givenName>
<gd:familyName>DifferentLast</gd:familyName>
<gd:fullName>SameFirst DifferentLast</gd:fullName>
</gd:name>
<gd:phoneNumber rel="http://schemas.google.com/g/2005#mobile">[phone]</gd:phoneNumber>
<gd:email rel="http://schemas.google.com/g/2005#work" displayName="SameFirst DifferentLast" address="SameFirstDifferentLast#example.com" />
<link rel="http://schemas.google.com/contacts/2008/rel#photo" type="image/*" href="https://www.google.com/m8/feeds/photos/media/example%40gmail.com/realcontactidhere?v=3.0"/>
<link rel="self" type="application/atom+xml" href="https://www.google.com/m8/feeds/contacts/example%40gmail.com/full/realcontactidhere?v=3.0"/>
<link rel="edit" type="application/atom+xml" href="https://www.google.com/m8/feeds/contacts/example%40gmail.com/full/realcontactidhere?v=3.0"/>
Strangest thing I have seen... not sure where to go from here. Any suggestions?

Answer 1

Solution that only took all day to figure out:
When changing a contact name only, and nothing else, the displayName property needs to be removed from the XML you are sending to Google.
This will succeed:
<gd:email rel="http://schemas.google.com/g/2005#work" address="SameFirstDifferentLast#example.com" />
This will fail:
<gd:email rel="http://schemas.google.com/g/2005#work" displayName="SameFirst DifferentLast" address="SameFirstDifferentLast#example.com" />