A married couple living on Brisbane's bayside had realized their credit card dues were being paid off automatically, but instead of reporting the suspicious mistake, they took it as a windfall and enjoyed the luxury they could afford with it, until they were jailed for having done so.

David and Deborah Palmer used their Visa card for six years to pay for a new car, jewellery, furniture and other luxury items that their windfall could easily cover, Brisbane Times reported.

Mr and Mrs Palmer also used the credit card to support their gambling for leisure.

Mrs Palmer first applied to the Bank of Queensland for the credit card in May 2002. She was 51 at the time, and her husband, a former navy and air force officer, was 48. They were going to use the credit card to buy a lawnmower to kick off a mowing business.

When they went back to the bank to pay off their balance, they were surprised to learn that their outstanding balance was just $375.

They told the teller it was not possible, but without realizing the details behind their reaction, the teller told them: "Computers don't lie." In turn, the couple did not say anything more.

From that time on, the couple had begun to splurge using their credit card, which effectively became their "magic beans."

Gradually increasing their credit limit, the Palmers had spent over $313,000 using the credit card by July 2008. Add to this the card's interest, the couple's unknown sponsor had paid over $344,600 in credit card bills.

The couple later discovered their unintentional "sponsor" was Palmer Steel Trading, which is based in Stapylton, south of Brisbane. It was only in 2008 when an audit of the company revealed the company was making monthly payments to a credit card account that does not belong to the firm.

Palmer Steel Trading then complained to the Bank of Queensland, which, in turn, contacted police authorities and later reimbursed the company.

The Palmers were then arrested, and they subsequently admitted they knew their windfall was most likely the result of a computer glitch.

The couple had sold their house in Thornlands and had managed to repay the bank $312,000.

Judge Kiernan Dorney QC said the Palmers were a ''sad case,'' and he sentenced the couple to four years' imprisonment.

However, as both Mr and Mrs Palmer both had no other criminal recprds, Judge Dorney ordered the sentence be suspended after the couple had spent 11 months behind bars.