Lots of the academic types don't like high yield bonds of any type, especially wrt diversification. They tend to be highly correlated to stocks since when the market tanks, defaults go up.
I've also heard that the AMT hit on those munis can potentially reduce your yield, but I haven't looked at that fund in detail.
But as long as you understand what you've got there and it works for your situation, I don't see any reason to sell.
Favorite ERF quote: "I'm not going to waste my time on someone who's more interested in being stubborn or obtuse or intolerant." -- Nords
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