In gambling, they say the house always wins. But for seven weeks this summer at Twin River, apparently that wasn’t true.

One of the Lincoln gambling parlor’s 4,700 video lottery terminals was instantaneously doubling gamblers’ money, giving them a credit for twice what they’d put in.

The machine was issuing credits for double the amount of whatever patrons inserted up to a maximum of a $100 credit for a $50 bill, said Robert Vincent, a spokesman for GTECH, the company that supplied the machine. Patrons could redeem the credit without playing a game.

It was, says Robert M. Silva, legal counsel to the Rhode Island Lottery, “a gambler’s dream.”

GTECH removed the machine on July 15, as soon as the malfunction was discovered. But by that time, it had paid out $450,115 more than it should have.

GTECH has reimbursed the state for that amount, officials with the company and the state said yesterday. Now, GTECH is mounting its own investigation to examine how the malfunction happened and whether it might have been discovered sooner.

The company will try to determine whether criminal activity took place and whether GTECH stands to recoup any of the lost money, company spokesman Vincent said.

Vincent said the machine in question offered a game called “Passion Coast,” and that it was one of 299 machines at Twin River manufactured by Atronic. He said the machine apparently malfunctioned from the day it was installed — May 25 — and that it appeared to have been installed with the money-doubling feature turned on by accident. The feature can be used to double patrons’ winnings on purpose as part of a promotion, Vincent said. He said GTECH has ascertained that none of the other similar machines had the same feature turned on.

The local NBC affiliate, WJAR Channel 10 — which broke the story Wednesday — said the malfunction was reported to Twin River security by a patron. Vincent said he could not confirm that, and that GTECH shut down the machine after noticing that a key ratio for the machine was higher than it should have been.

The company gets regular reports on all the machines it supplies, but a high ratio “doesn’t immediately trigger an alarm” because one very large payout might temporarily push up a machine’s ratio, Vincent said. Only if the ratio stays elevated does it become clear something is amiss, he said.

As to reports that people were lining up to use this machine in particular, Vincent said: “If something like a lining up were happening, security would take notice of that,” and the malfunction would have been discovered sooner. “I suspect that probably wasn’t the case,” he said.

Vincent said Twin River did not collect personal information from the people who redeemed the credits because the credits fell below the Internal Revenue Service’s $1,200 reporting threshold for gambling winnings. But he said GTECH has obtained surveillance video showing players using the machine.

Michael J. Healey, spokesman for Attorney General Patrick C. Lynch, said the potential for bringing criminal charges exists, “particularly if there could be established a pattern of people or of a person going back to the VLT in question again and again.”

As senior director of global security at GTECH’s headquarters in Providence, Steven M. Pare, former head of the Rhode Island State Police, is overseeing the investigation.

The state police are not involved. “We have no criminal investigation being conducted at this time,” Maj. Joseph R. Miech said yesterday. “There’s been no criminal complaint filed.”

Since the $450,115 represents money the gambling parlor should have kept, but didn’t, the state will parcel out portions of it to Twin River, GTECH and the Town of Lincoln, as is the practice with all the money gamblers lose at Twin River. The gambling parlor will get $123,000; GTECH will get back $43,000; the Town of Lincoln will get $6,000; and the state will keep $274,000. Another $4,000 will be set aside for the Narragansett Indian tribe.

This year’s $7-billion state budget includes more than $271 million in revenue from the video slots at Newport Grand and Twin River, which until March was known as Lincoln Park.

Silva, of the state lottery, said there have been erroneous payouts in the past. He cited an overpayment of $300,000 in 2005, one of $27,000 in 2003, and one of $51,000 in 1998.

“There are occasions when computers break down and malfunctions take place,” he said.

Both Silva and Twin River spokeswoman Cynthia Stern said they are satisfied with GTECH’s monitoring of the machines’ performance.

“Everything’s being paid back. Everybody’s working in cooperation,” Stern said. “We have a very collegial relationship and we look forward to that continuing.”

egudrais@projo.com