ANZ Bank's accounts show its new mortgage lending to people with small deposits apparently ballooned in the September quarter.
However, New Zealand's largest bank says its own published numbers don't reflect what actually happened.
ANZ's accounts for the June quarter showed a very low level of lending to people with deposits of less than 20%.
Just 3.2% of net new mortgages in the three months, or $29 million, was lent to those customers.
The bank's accounts for the September quarter show a whopping 22.5%, or $198 million, of net new mortgage lending was to people with deposits of less than 20%.
Radio New Zealand's business editor says the bank has given only cursory answers to questions since Thursday last week.
It says it made adjustments to historical lending loan-to-valuation classifications in its June quarter accounts but there is no mention of these adjustments.
The bank says that, therefore, it isn't valid to compare the June quarter accounts with the September quarter accounts.
ANZ says, generally, it saw a decline in high loan-to-valuation lending across the six months.
Explain adjustments - Tripe
David Tripe, the head of banking studies at Massey University, says ANZ should spell out exactly what adjustments it made and how to reconcile the figures so they make sense.
"There does appear to be some problem and there's some confirmation of that from the ANZ having advised that there has been some adjustment made."
Mr Tripe says the public and holders of ANZ debt will want to know details of any adjustments that have been made.
Since 1 October, no more than 10% of each bank's total mortgage lending can be to people with deposits of less than 20%.