With valuations on U.S. stocks high in the eyes of some market observers, the previously positive impact of share buyback programs is being muted, triggering some rare under-performance by companies that have been voracious buyers of their own shares.

“Firms with larger buybacks outperformed the market for several quarters, but that streak is in jeopardy, as the S&P 500 Buyback Index is down 0.2 percent for the quarter,” report Caroline Valetkevitch and Chuck Mikolajczak for Reuters.

The PowerShares Buyback Achievers Portfolio (NYSEArca: PKW) is down about 1% this quarter compared to a 0.7% gain for the S&P 500. PKW tracks the NASDAQ US Buyback Achievers Index, not the aforementioned S&P Buyback Index.

Some of PKW’s second-quarter struggles can be tied to its large consumer discretionary of almost 34%. Although discretionary firms have been among the largest repurchasers of their own shares in recent years, the sector has struggled this year with the Consumer Discretionary Select Sector (NYSEArca: XLY) and the Vanguard Consumer Discretionary ETF (NYSEArca: VCR) down an average of 3%.[Returning Retail ETFs]

S&P 500 companies that initiated buybacks in the first three months of 2014 underperformed the benchmark index by 0.25 percent in the month after announcing, while a similar group outperformed the index by 1.29 percent in the same period a year ago,” Reuters reported, citing Birinyi Associates.

One quarter, one that is barely half complete at that, of under-performance is not a reason to write-off PKW. The ETF’s long-term track record and that of its underlying index confirm as much.