(Bloomberg) -- A mystery has underpinned recent comings and goings of money in the $1.3 trillion U.S. high-yield bond market.

Over the past month, the biggest junk-bond ETF has experienced extraordinary record-breaking daily withdrawals even though the broader market has encountered relatively little turbulence. In fact, these ETF flows have had little to no correlation with mutual-fund deposits or other gauges of investor demand. They are often followed or preceded by huge deposits.

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