I work at a bank underwriting loans. I was going to say it may be fees that have been added to the principal balance of the loan during the course of the loan term (fees can range from late fees, title work fees, appraisal fees etc). Depending on how the loan is set up, in most situations when you roll those fees into your principal balance, then you are also paying interest on the fees + current principal balance which makes it grow pretty fast as you can imagine