Impossible Update Product without delete any XML-Nodes

[roccomedia]

I´m doing a normal PUT-Command to update a single product but during this action the response message called ("parameter "position_in_category" not writable. Please remove this attribute of this XML"). I have deleted these XML-Node after this the same error comes with the "manufacturer_name" Node. I´ve deleted too. The response was "Succesfully" but now the Node with the Value of "Price" will be increased by every request approx 92 Euro..184.. This result happens becouse deleting of SimpleXMLnode with UNSET leave gaps in the XML-Structure. Can anyone help me to find a solution?? Thanks!