I am pretty sure you need to manually enable it on AdCenter.
Not sure how prosper wants you to set them up, but it should basically be using the right parameters in the right places.
Here is something from adcenter help:
Syntax and types of query string parameters
A query string parameter consists of a variable name and value in this form:
where variable is the name of the variable used in your company's script programs to identify the query parameter, and querytype is one of the following values:
* QueryString: Returns the text string that was typed by the search user
* MatchType: Returns the type of match (exact, phrase, or broad) that triggered the display of your ad
* OrderItemId: Returns the keyword that was matched to the text string
* AdId: Returns the ID number of the clicked ad
Here is a link to help you figure it out:
Go there and type in tracking. (adcenter help area)