A rally in Treasury bonds spurred mutual funds such as T. Rowe Price and Putnam Investments to trim their MBS holdings, but analysts say investors are concerned about more than just a new mortgage refinance boom. They’re also worried about credit quality. While Price and Putnam may be buying fewer lower-rated MBS these days, Pacific Investment Management Co. is still in the market. Under a new Pimco acquisition strategy, MBS account for 55 percent...