The Reserve Primary Fund's "breaking the buck" in 2008 sent investors in the $2.7 trillion money-market mutual fund (MMF) market running for the exits and regulators reaching for new rules to safeguard the short-term investments. More than three years later, the Securities and Exchange Commission's expected proposals for additional safeguards are running into vehement opposition.

The premise of stability was shattered when the net asset value (NAV) of the Reserve fund dropped below $1 a share and investors rushed to redeem their shares. The U.S. Treasury quelled the run by offering to insure MMF holdings.

In 2010, the SEC passed MMF amendments that increased liquidity requirements, reduced maturity limits and called for more disclosure. And it promised more rules to reduce the threat of runs on MMFs.