Lenny2, I don't think you should be seeing that. IBill will deduct a 10-15% fee and holds 5-10% for six months from the sponsors portion of the income. The only thing IBill deducts from affiliate checks are chargebacks and refunds.
Some information about iBill's revshare program can be found here:
http://www.ibill.com/services/revshare/
The document that explains exactly how the payouts work is called 'Revshare Program Functionality'. Unfortunately it does not appear to be linked off their website.