If credit unions are having trouble growing their mortgage services, that might be because most consumers really don't understand the mortgage contracts they need to use when buying a house.

Even after the housing finance industry has largely retreated from so-called exotic or complicated mortgage products, most home buyers still don't understand the plainer and simpler contracts that have come to dominate the real estate market.

Sponsored by Zillow Mortgage Marketplace, an online mortgage resource, the survey found, for example, that 57% of home buyers responding to the survey confessed that they did not know how adjustable rate mortgages work.