If the bank (and customer) did not pay the full amount, there could be a problem, as in many locals, the mortgage is "legal" only if the right amount of stamps is affixed. If the bank had to foreclose on the mortgage, it may be possible that there could be an issue as not properly recorded. I would (like others said) pay the amount, train and move on.
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Integrity. With it, nothing else matters. Without it, nothing else matters.