So with the normal cost of taxes and insurance you have a 38% debt ratio. Yes it should rock. The fact that you are asking the question leads me to believe that there is something going on.
1. It could be that there are additional taxes such as assessment district taxes
2. There could be association fees
These two items could raise the debt to income ratio and cause the ratio to go over 45% and cause a problem.
Another thing that happens is that the borrower may have answered an ad, advertising an interest rate that does not exist, several large companies do this. In order to make the loan with out losing money they have to claim that there was some reason the buyer did not qualify for that loan. Real sad, happens all of the time