Bill Gross, manager of the world's biggest bond fund, shook bond markets in June when his firm PIMCO, amassed an unusually large amount of June 10-year futures contracts.

NEW YORK (CNN/Money) - Bond investors and regulators are eyeing an imbalance in the Treasury market, worried that a shortage of bonds, which cost some investors hundreds of millions of dollars in June, could occur again in September, according to a published report.

But the article in The Wall Street Journal also said many market participants and regulators believe that increased attention to the market will prevent problems this time around.

The paper said the June losses happened after one of the world's largest bond-fund managers, PIMCO, had amassed billions of dollars of 10-year Treasury futures contract due for delivery that month, and other investors feared the firm would demand the bonds. That drove up the price of the 10-year bonds at that time.

The paper reports that PIMCO had bought as much as $14 billion of June 10-year futures, although the firm hasn't given any numbers. Typically, the fund's managers would simply trade those contracts for September contracts, the paper said. But with the price of the September contracts having risen so much, the trade became prohibitively expensive, according to the report.

Since futures contracts come due every quarter, the next shortage could be seen in September, according to the paper's report.

Concerns about what happened in June has produced a "lot more clamoring" for bonds that are needed to close out 10-year futures contracts, James Bianco, head of bond-research firm Bianco Research, told the Journal.

"It's a technical problem that's growing, and it's not going to get better," he said.

But some others who talked to the Journal believe that the problem won't be as severe this time.

"I think the amount of market and regulatory scrutiny would deter any predatory activity," says Jason Evans, head of Treasury trading at Deutsche Bank Securities in New York.

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