This is normal and shoudn't affect reporting. When adding an argument to the URL, such as the "s_src=xxx" argument, the argument is added to the user's session. The argument remains a part of the user's session throughout the session regardless of whether or not that argument remains in the URL.

For example, go to a donation forms.  Then fill everything out but use a bogus credit card, say 4111 1111 1111 1111, and try to process the donation, eventually the URL will become something like:

https://secure.convio.net/shortname/site/Donation2

The df_id argument is gone. The s_subsrc is gone. All of the arguments are gone but the system still knows what donation form you are working with, etc. because of the session that has been established.