Only half of the millions of underwater homeowners who have been frozen in place for years are still interested in homeownership once they rise to the surface. The so-called “Boomerang Buyers” may turn out to be a boomerang bust if a new study from NAR is accurate.

According to CoreLogic’s first quarter equity report, some 9.7 million, or 19.8 percent, of all residential properties with a mortgage, were underwater. This figure is down from 10.5 million, or 21.7 percent of all residential properties with a mortgage, at the end of the fourth quarter of 2012. The underwater percentage of homeowners with a mortgage reached as high as 30 percent in 2010. Negative equity, often referred to as “underwater” or “upside down,” means that borrowers owe more on their mortgages than their homes are worth. Negative equity can occur because of a decline in value, an increase in mortgage debt or a combination of both.

The huge cohort of underwater homeowners took millions of potential listings off the market in recent years and contributed the inventory shortages driving up prices in the first half of the year. Though the ex-upside down owners may be sellers, only half plan to buy again. A survey of several thousand Realtors released today by the National Association of Realtors found that among Realtors who reported working with an underwater homeowner seeking to sell a home, only 53 percent of newly above-water owners were planning to buy another home and 22 percent intend to rent, but 25 percent weren’t sure what they’d do.

The loss of 5 million or more homeowners from the nation’s 76 million homeownership households could national homeownership rate significantly. An additional 47 percent of Realtors in the NAR study said that they have potential sellers who are waiting for additional price appreciation before they sell. No doubt these are among the 39 million residential property owners with positive equity, 11.2 million of whom have less than 20 percent equity. Borrowers with less than 20 percent equity, referred to as “under-equitied,” may have a more difficult time obtaining new financing for their homes due to underwriting constraints. At the end of the first quarter of 2013, 2.1 million residential properties had less than 5 percent equity, referred to as near-negative equity. Properties that are near negative equity are at risk should home prices fall. Under-equitied mortgages accounted for 23 percent of all residential properties with a mortgage nationwide in the first quarter of 2013, according to CoreLogic.