This problem was reported to us as a bug and it can be reproduced. I created a bug for maintenance (https://tempo-io.atlassian.net/browse/TMA-12091), but is was withdrawn with the explanation:
"This endpoint is not supporting partial updates and is also internal.
You could create a feature request for public account api with partial updates."
This REST API is documented in our public documentation, see https://www.tempo.io/server-api-documentation/accounts#operation/updateAccount
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