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Here is an article that points toward the potential for problems with high yield bond ETFs:
Investors Playing ETF Rout Pushed Junk Bonds to Brink of Chaos.
Excerpt:
Trading in exchange-traded funds got a little crazy last week when it became clear that junk bonds were in for more pain. But the market was fortunate the consequences weren’t more severe, strategists warn. Though spared the worst, investors came close to creating a scenario where ETF activity drove prices....a snowball effect where a dislocation develops between the fund price and the value of its underlying assets.