Olof,
I downloaded 2.2a Contrib and im having this exact same issue. I am not an expert by far but, can you change the MATC to the checkout_payment.php page? this will work I think... also I found another contribution that has solved (they say) java disbled issues.
http://www.oscommerce.com/community/contributions,1341
does it work?
Also something important for Caludio, as he says its must: Is there any way to record in the Orders and Clients DB that the client has accepted the T&C? This can be very helpful for example as a defense in case of any problem with bank or reversed operations... :)
I had to make a full roll back of MATC because of PayPal problems :(