Right now I have this simple test form:

{exp:channel:form channel="data" category="6" status="Closed" return="contact/thanks" }
   <input name="title" type="text">

   <input type="submit" value="Submit">
{/exp:channel:form}

The data is submitted but it doesn't set the status or the category. Maybe I am misunderstanding the documentation on how this should work.