Secondary bond market

A possible explanation is that the massive inflows into mutual funds are a parallel move to large inflows into the Capital Group Municipal High-Income ETF, which saw the biggest inflow of a ETF on Friday at $1.5 billion, said Pat Luby, head of municipal strategy at CreditSights.

FOMC meeting minutes "clearly show why they didn't cut rates," said Northlight Asset Management Chief Investment Officer Chris Zaccarelli.

The muni bond market remains strong, supported by Treasury market strength, said Anders S. Persson, Nuveen's chief investment officer for global fixed income, and Daniel J. Close, Nuveen's head of municipals.

"If unfavorable economic numbers ... are released next month, we should expect a hold on any rate cuts and a possible rate hike to follow, putting a damper on any positive returns for the rest of the year," said Jason Wong, vice president of municipals at AmeriVet Securities.

Issuance for the week of Aug. 18 remains elevated at an estimated at $6.166 billion, with $5.065 billion of negotiated deals and $1.101 billion of competitive deals on tap, according to LSEG.

The latest inflation report — the producer price index — threw a monkey wrench into expectations for a big rate cut next month, according to some economists, may put into question any easing in September.

Muni performance is likely to recover during the second half of the year, said Cooper Howard, a fixed income strategist at Charles Schwab.

Through June 30, BAM insured 11 transactions with par of $100 million or more, with four more deals coming since then, the company said.

"The combination of stronger core and softer headline readings has left some traders struggling for direction," said Daniela Sabin Hathorn, senior market analyst at Capital.com. "There is a reason to be both bullish and bearish depending on which CPI reading you wish to focus on."

Returns for the month currently stand at 0.64%, which have "pushed muni returns back into the green with year-to-date returns of 0.09%," said Jason Wong, vice president of municipals at AmeriVet Securities.