The continuing quest for yield at a time of low and negative interest rates is causing tumult in an unlikely corner of the market.

Certificates of deposit, a fairly sacrosanct investment where capital is preserved on the promise of modest but positive returns, are in some cases leaving investors flustered. A comparatively new and increasingly popular product known as a "structured" CD is luring investors with promises of better-than-normal returns that often fall short, according to a report Wednesday in The Wall Street Journal.