Rest Api does not update returned datasource after action call

After calling an action, I want to update the datasource associated to this action.
This seem to work fine appNG internal application but does not work on the Rest Api.

I have attached an example project.
the DataProvider for a single Person will always set the value of two fields "writeField" and "readField" to a specific value.
In the updateAction, the client changes the value of "writeField".
the results of the PersonXmlTest and PersonRestTest are different. In the firt test, the value gets changed back to the server text while in the second test, the value of the client remains.