1) The bank has no liability.
2) Postal money orders can be returned by the US Postal Service for months:
"The postmaster general has the right to demand refund from the presenting bank of the amount of a paid money order if, after payment, the money order is found to be stolen, or to have a forged or unauthorized endorsement, or to contain any material defect or alteration not discovered on examination. Such right includes, but is not limited to, the right to make reclamation of the amount by which a genuine money order with a proper and authorized endorsement has been raised. Such right must be exercised within a reasonable time after the postmaster general discovers that the money order is stolen, bears a forged or unauthorized endorsement, or is otherwise defective."
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The opinions expressed are my own, take them or leave them.