(Bloomberg) -- Low-volatility funds are supposed to insulate investors from the market's bouts of turbulence. Lately, that's been flipped on its head.

For six weeks, the most popular low-volatility ETF has experienced price swings that were wider than the broader market. While not the first time it's happened, never before has it gone on this long. BlackRock's iShares Edge MSCI Minimum Volatility ETF has traded with higher volatility than the S&P 500 for 42 days, eclipsing the old record of 16.

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