The iShares 0-5 Year High Yield Corporate Bond ETF (SHYG) has lost $1 billion in assets over the past week. A robo-advisor operated by a major brokerage is seen as the culprit behind the outflows from the high-yield debt exchange-traded fund (ETF).

SHYG's "biggest listed owner is discount brokerage Schwab, with more than 38% of the shares worth $1.4 billion as of March 31," reported The Wall Street Journal. "Schwab uses the iShares fund in the prepackaged ETF portfolios sold through its robo-advisory division, Schwab Intelligent Portfolios, according to its website."

SHYG, which tracks the Markit iBoxx USD Liquid High Yield 0-5 Index and holds 626 bonds, had $2.87 billion in assets under management as of June 6, according to issuer data. The ETF has an effective duration of 2.41 years and is the shorter duration answer to the iShares iBoxx $ High Yield Corporate Bond ETF (HYG), the largest corporate bond ETF. HYG's effective duration is 3.84 years. (See also: An Introduction to Corporate Bond ETFs.)

The position in  SHYG liquidated by The Charles Schwab Corporation's (SCHW) robo-advisor is being moved to the iShares Broad USD High Yield Corporate Bond ETF (USHY). USHY, which debuted in October, offers investors a broader representation the domestic junk bond market. The ETF follows the ICE BofAML US High Yield Constrained Index and holds nearly 1,600 bonds. USHY's effective duration is 4.16 years.

Broadly speaking, corporate bond funds are falling out of favor this year as investors bet that the Federal Reserve will continue hiking interest rates. Year to date, three of the 10 worst ETFs in terms of assets, including HYG, are corporate bond funds. The iShares iBoxx USD Investment Grade Corporate Bond ETF (LQD), the largest corporate bond ETF, has shed $4.72 billion in assets, a total surpassed by just two other ETFs. (For more, see: Should You Invest With Junk Bond ETFs?)

SHYG allocates about 83.8% of its weight to bonds rated BB or B, but the fund also devoted 13.5% to highly speculative CCC-rated debt. USHY, the fund that Schwab's robo-advisor moved to after departing SHYG, is not significantly better in terms of credit quality. That ETF allocates about 85% of its roster to bonds rated BB or B, and its CCC exposure is 12.8%.

Recently, Goldman Sachs said that the credit risk premium assigned to CCC-rated bonds fell to its lowest levels since the global financial crisis, indicating that there is not much value in the most speculative of junk credits. (For additional reading, check out: Bets Against Junk Bond ETFs Reach Record High.)