Actually never happened to go thru the list of properties available for the request type. Thanks for that.
Here is what I notice.
If you have an element of a soap request which is mandatory and value has not been provided, the element is removed from the request on looking at raw xml.
Tried with element which has an optional attribute, kept the value empty. In the raw request found the attribute is removed.
Also found in another test that an element has 3 attributes allowed and 1 specific attribute is mandatory. Kept all the attribute values empty. When send the request, it has randomly kept one attribute in the request. So, for me it seemed like you running into this case. May be you can have one more check with other requests and see.
Also you try validating your request by right click or key in Alt+v, then you will come to know in first place whether your request is correct and all mandatory elements/attributes are there.
