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@mrbiggiesmalls To reiterate what was said in both an answer below previously and what @Zbucklyo  reconfirmed:
the imputed (and ultimately paid out in the form of the increased sale or maturity price) interest on a tax-exempt bond is indeed tax-exempt.  However, the difference between the contantly-revised cost basis (as thoroughly discussed in both answers and @msdalt01 's calculations) and the actual proceeds of selling the bond (or a call price if called) will result in possibly taxable gain or reportable loss.  It is not only permissable to report the capital loss, you do yourself no favour by failing to do so.
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