To be sure, the negative yield bond investment strategy could backfire if central banks disappoint market expectations in some way. In late July and early August, the 10-year Japanese government bond yield went from negative 0.3 percent to almost zero after the Bank of Japan, contrary to expectations, did not increase government bond purchases.
In February, BlackRock's Rieder told CNBC that negative interest rates have diminishing benefits the longer they are in place and should be seen as a short-term effort during situations such as a financial crisis.
But "when you breach zero, you're taking money from savers, you're taking money from the banking system … and I don't see who you're handing it to," Rieder had said.
Regardless, investors still like the security of fixed income. U.S.-based taxable bond funds saw their fourth week in five of positive fund flows in the week ended Sept. 7, with gains of $3.4 billion in cash, Thomson Reuters Lipper data showed Thursday.
In contrast, U.S. stock funds posted their third-straight week of net withdrawals, with $271 million in outflows last week, according to the data.
Morgan Stanley's Chief U.S. Equity Strategist Adam Parker noted in a Thursday report that "it's a tough time to be an equity portfolio manager" as various investment strategies based on factors such as market cap did not significantly outpace markets in the last few months.
Meanwhile, investors remain concerned about market shocks from slowing global growth, a potential Fed rate hike, the U.S. presidential elections, political uncertainty in Europe and China's struggle to manage an economic slowdown.
"From a positioning standpoint, we don't think now is the time to take on a lot of risk," Michael Fredericks, portfolio manager of BlackRock's Multi-Asset Income Fund, said during Wednesday's roundtable. He said the level of risk exposure is one of the firm's lowest in years, and he's been cutting back on stocks and acquiring bonds such as emerging market debt.
"For the amount of risk and volatility you take in equities, you're going to do pretty well or just as well in fixed income," he said.
The negative yield phenomenon isn't just a development for the investing side. On Tuesday, two European companies — Germany's Henkel and France's Sanofi — became the first nonstate owned entities to sell negative-yielding nonfinancial corporate bonds in euros.
—CNBC's Patti Domm contributed to this report.