DPC Data is one of four firms recognized by regulators as municipal securities information repositories. For the study, Peter J. Schmitt, DPC’s chief executive, examined trades that involved issuers that had recently filed so-called distress notices, indicating that they were experiencing financial problems.

Mr. Schmitt found that an alarming number of these beleaguered issuers’ securities were purchased by individual investors at nondistressed prices  100 cents on the dollar (known as par value) or higher. This indicates that brokerage firms executing the trades may not have been aware of the issuers’ troubles or failed to give investors full disclosure about them, Mr. Schmitt said.

“The fact that these rules, which were meant to stimulate disclosure, have been swept under the rug and that the market has been allowed to go forward on poor and inconsistent information doesn’t say a lot about how assiduously regulators are pursuing investor protection,” Mr. Schmitt said.

It comes as no surprise that defaults and other stresses on municipal issuers rose significantly in 2008 as the credit crisis deepened. Some 348 distress notices were filed last year, up from 187 in 2007.

Although the economy was tanking, DPC data found that almost 28,000 trades took place in securities that issued a distress notice at some time during the year. Some 9,643 of those trades were sales to customers, both institutions and individuals; more than half of them  5,798  were bought at par value or higher.

Mr. Schmitt dug deeper, analyzing how many customer purchases were made after a distress notice was filed by the issuer. He found 1,782 such trades, of which 667 were sold at par or more.

Obviously, when evidence emerges that a debt issuer is under stress, one would expect the price of its bonds to fall. And yet hundreds of trades of exactly this kind of debt were priced at par or higher, which Mr. Schmitt finds troubling.