The reason: a lack of a change of control covenant, something that unfortunately for the debtholders did not become in vogue until the LBO boom of 2006 to 2007, according to a recent report from Moody's Investors Service Inc.

These covenants "did exist before the LBO boom, but they became much more prevalent in the years after that, starting in 2006 and 2007," said Alex Dill, Moody's head of covenant research.

Almost $900 million of H.J. Heinz Co. will likely end up heavily subordinated following the buyout, the Moody's report said. In fact, on Tuesday, Moody's rated this debt, which will be assumed by Heinz at B2, one step below the $2.1 billion of senior secured second-lien notes and three steps below the proposed $10.5 billion senior secured first-lien loan package.

J.P. Morgan and Wells Fargo & Co. have launched the syndication of the $12 billion loan component of the financing. The banks are holding a meeting in New York to kick off the loan financing on Thursday, March 14, with a London meeting to be held the next day, according to Reuters' LPC. Heinz went out to the bond market with an offering of $2.1 billion of 7.5-year notes on Wednesday, according to data provider Thomson Reuters. The notes are expected to price late next week or early the week after. Joint bookrunners on the notes are Wells Fargo, J.P. Morgan, Barclays and Citigroup.

If LBOs pick up this year, especially blockbuster deals like Heinz, there could be more debtholders finding themselves in the same position: witness the $24.4 billion Dell Inc. buyout where investors hold bonds of 30-year or longer maturities.

However, at least one asset manager holding some of the Heinz debt said the firm will likely maintain its position based on the yield from the notes, which beats most debt offerings available in the days of a Federal Reserve interest rate close to zero. Plus, there's the magic bullet of Buffett's reputation that is likely to keep debt holders from dropping these notes.

That might not always be the case, said Michael Chernick, a partner at Paul Hastings, who pointed out that Buffett is putting up $8 billion in preferred shares as part of the deal. Other buyouts might not be so friendly to asset managers holding debt without COC covenants.

"A lot of that (comfort level) is probably people saying it's a Warren Buffett company," Chernick said. "Even though the company is going to be more levered, he knows how to operate a big company like this."

In addition to the $8 billion in preferred equity from Berkshire Hathaway, the two companies are both offering $4.12 billion in common equity.

In the Heinz deal, Moody's said three tranches -- notes issued between 1998 and 2003 -- do not have change of control covenants and could be rolled over into the new company without being replaced by new debt.

Because of the amount of leverage involved in the buyout, it is expected that the status of these notes will change from investment grade to high yield, which is likely to lead to much lower prices for the notes. Fitch Ratngs already downgraded the company's senior unsecured debt BBB+ to BB+.

The debt adds up to approximately $870 million on what is expected eventually to be a company that has a total debt load of $12.5 billion. It consists of a $250 million issuance of 6.375% debentures due in 2028 that has $235 million outstanding, a $550 million issuance of 6.75% senior notes due in 2032 that has $436 million outstanding and an issuance of £125 million ($187.7 million) of sterling-denominated 6.25% notes due in 2030.

Prices on the dollar-denominated bonds have already dropped steeply since the deal was announced. The 2028 debentures sank from 115.2 the day before the buyout announcement to 105.5, according to data from Finra's Trace. The price on the 2032 notes decreased from 126.9 to 106.5.

Three debt holders have substantially more invested in these tranches than other investors, according to data provider Thomson Reuters. Western Asset Management owned $34 million of the 2028 debentures as of Dec. 31, 2012; M&G Securities Ltd. owned $33.2 million of the 2013 notes as of Dec. 31, 2012, and Unum Group owned $14.6 million of the 2032 notes as of Dec. 31, 2012.

Western Asset did not respond to a request for comment. M&G Securities and Unum Group declined comment on their holdings.

One asset manager whose firm holds some of this debt, said the firm will likely hold onto the debt because of the higher yields on these bonds versus what is available in the current high yield market.

"We're not too happy with them going below investment grade, but it's a good company and it's going to be run well," the source said. "You've got Warren Buffet involved. They're long-term investors. That makes us feel better about the situation."

Changes from investment grade to high yield due to LBOs has not happened much since 2007 because the economic environment has not been particularly LBO friendly, the source said. However, in the long run, bond downgrades are something that happens, especially to longterm investors. "It's just one of those cyclical things."