BlackRock Inc’s iShares Gold Trust IAU may face penalties and other costs after the U.S.-listed fund sold $296 million in shares of the exchange traded fund earlier this year without properly registering them, the company said in a filing on Monday with the U.S. Securities and Exchange Commission.

The fund manager, describing the problem as “inadvertent,” said it would immediately resume issuing shares in the $7.8 billion fund after suspending such issuance last week.

The BlackRock affiliate that supervises the Gold ETF said it may be required to re-acquire nearly 25 million shares of the fund it issued between Feb 19 and March 3, in excess of the shares it had officially registered with federal authorities. Those shares were worth $296 million when they were transferred, the filing said.

BlackRock said investors who bought and resold the unregistered shares “may have the right to collect damages” plus interest from the fund, and that the company may also have to pay SEC and state penalties. The fund may have to sell gold to meet those obligations.

On March 3, after realizing the error, BlackRock stopped selling new shares of the fund – which trades like a stock on an exchange but is meant to reflect the precious metal’s market value. The BlackRock fund and its shareholders actually own gold, the commodity, rather than shares of gold-mining stocks or any other proxy.

Investors have flocked to gold and related financial products as economic uncertainty, a weak dollar and falling expectations for U.S. interest rate hikes have spurred the biggest buying spree of gold ETFs in five years.

The filing does not disclose how much compensation for loss might be required or what penalties might be imposed, and representatives for both BlackRock and the SEC declined to comment for this story.

“I’m not familiar with any precedent for the sale of unregistered shares of an exchange-traded product,” said Ben Johnson, director of global ETF research at Morningstar Inc , who said the episode highlights the importance of understanding differences between various types of funds. “Not all exchange-traded products are created equal.”

On March 3, the fund closed at $12.17 a share. On March 4, when BlackRock issued a press release noting the share freeze, it rose as high as $12.37 before closing at $12.17, a discount to the fund’s $12.33 net asset value.

Exchange-traded products (ETPs) trade throughout the day at market-determined prices. When they restrict creation of new shares, the funds often start to trade at a higher price than the “net asset value” of the investments the fund.

The gold ETP is registered under a different legal structure than most exchange-traded funds, which do not have to register new securities in as cumbersome a manner.

So far this year IAU has delivered a 19 percent return, according to Lipper, and its assets under management have surged by $1.4 billion to $8 billion since the start of the year. The fund traded up 0.6 percent Monday afternoon in New York.