Getting Request has invalid or unsupported property when trying to save preferences

I am trying to update some preferences, I fetch the current preferences, modify what I need to modify, and send it back. However this fails with this response.
```
"response": {
"Fault": {
"Error": [
{
"Message": "Request has invalid or unsupported property",
"Detail": "Property Name:failed to parse json object; a property specified is unsupported or invalid",
"code": "2010"
}
],
"type": "ValidationFault"
}
```

Start by reproducing the fetch-modify-save preferences flow described in the issue and inspect how the SDK serializes the returned preferences into the update request. Identify the unsupported or invalid property causing error 2010; done means the modified preferences save successfully without the validation fault.

Written by the indexing model from the issue text.