Don't blame the summer selloff in municipal bonds entirely on rising Treasury yields and a Fed with an itchy trigger finger. It's also a matter of supply, said Mark Paris, head of municipal bonds at Invesco(IVZ) - Get Report . Paris, who co-manages the Invesco Municipal Income Fund (VKMMX) - Get Report , added that December and January tend to be big reinvestment months, but "we have to get there." New issuance may be weighing on municipal bond prices, however, international buyers have been helping on the demand side. Paris said foreign buyers like muni yields, especially compared to negative interest rates in some developed countries. Munis continue to be a "pure play" on the U.S. economy and have been insulated from global macro news, according to Paris, who favors essential service revenue bonds. He said the technicals continue to be strong and the U.S. economy's steady growth is good for the muni fundamental story.