The popularity of money market funds comes from the perception that they are as safe and stable as a bank account, with reliable albeit small returns for investors.

That image was shattered in 2008 when the Reserve Primary Fund — the largest money market in the nation at the time — “broke the buck” because its value fell below $1 per share, an event that disrupted the financial system and exacerbated the financial crisis. The government responded by temporarily guaranteeing that investors would be repaid.

Now, the Securities and Exchange Commission provides another reminder that these funds are not as stable as the average mom-and-pop investor may think.

The agency reported this month that nearly 160 money market funds have sought the SEC’s permission to shore up their funds using cash from their parent companies since 1989 — and that’s not counting the requests made during the financial crisis years.

Nearly a dozen events triggered the written requests, including headline-making events such as the bankruptcy of California’s Orange County in 1994. But the requests were not immediately disclosed. The SEC did not make such letters public before the 2008 financial crisis. Now, they’re made public on a delayed basis to avoid instigating a run on a fund.

“So investors may have been unaware that their money market fund had come under stress,” according to the SEC report, which did not name the funds involved.

The money market fund industry says these numbers present a warped view.

For starters, not all the funds that requested financial support ultimately needed it, a point that the SEC acknowleged. Even during the financial crisis, some of the funds that applied for and received permission to provide financing to their funds “never put a dime into their funds,” the industry said in a blog posting when similar issues arose in August.

Even when a fund’s sponsor does provide support, it’s not necessarily because the fund is about to break the buck, the industry said. And the SEC acknowledged that, too.

“Sponsors may support funds to protect their reputations and their brands,” the report said. “... One should be careful to avoid interpreting (the SEC findings) as evidence that funds seeking support necessarily would have broken the buck had it not been provided.”

For instance, a sponsor may buy downgraded securities out of a fund’s portfolios to maintain a fund’s top-notch credit rating, the industry said. In 2010, the year of the BP oil spill, the SEC cited three cases in which sponsors bought their funds’ BP securities. The funds did so to limit risks to investors, not because they were in danger of breaking the buck, the industry has said.

Still, if there were no real danger, why would sponsors seek to put their own money in their funds, said Robert Plaze, a 30-year veteran of the SEC who was deputy director of the agency’s investment management group until August.

“The staff would not have granted relief unless the company had demonstrated the need for relief, meaning that the fund was potentially threatened with harm,” Plaze said.

Take the credit rating example provided by the industry. If a fund lost its top credit rating, it’s plausible that investors would rush to withdraw their money from that fund and the fund could then ultimately break the buck, Plaze said.

The industry has said that even if one fund breaks the buck, it’s not likely to set off destabilizing runs like the one in 2008, and the SEC said that the events it cites as having affected money market funds “did not appear to cause systemic problems.”

But perhaps the larger issue is that investors have come to rely too heavily on having the sponsors kick in their financial support, Plaze said. After all, only two money market funds have ever broken the buck since these types of mutual funds were created.

“A 30-year history of fund managers always coming through is impressive,” Plaze said. ”It implicity has suggested that sponsor support will always be available. ... The problem is, nobody knows if the fund management can come up with the money in times of crisis.”

The SEC report comes at a time when the government is seeking tighter oversight of the $2.6 trillion money-market industry to avoid a repeat of the Reserve Primary Fund debacle. The near collapse of that fund prompted a run on money market funds that devastated the financial system. Top financial regulators have pushed to revamp the industry ever since, but the industry has pushed back.

SEC Chairman Mary Schapiro came up with a proposal, but abandoned it in August when she failed to rally the support of three of the commission’s five members, including Democratic Commissioner Luis Aguilar. He said the agency needed to study some issues more closely before moving forward with the chairman’s plan.

In response, the agency’s staff produced a study to address the three commissioners’ wide-ranging concerns. The study included the breakdown of all the incidents in which money market sponsors asked for permission to financially support their funds, outside the financial crisis years, defined as 2007 through 2009.