It was a down day for munis in general today. However, on a percentage basis, ORNAX got hammered. I think Ibench is correct, as the quality of holdings in the fund are largely rated junk status.
I'd be really careful about continuing to dollar-cost average into this fund until/unless there is some indicator that there is any demand for low-rated bonds in the marketplace. Buyers are skeptical, considering the ratings agencies have exercised such poor judgment in the past couple of years. There's no shame in hanging on to cash for a little while.