Why is the Wisconsin-specific interest included in Wisconsin state tax form?

On my Wisconsin state form Schedule AD, the State and Municipal Interest is not being reduced by the Wisconsin-specific interest earned. The Smart Worksheet shows the correct number on line a) (Interest earned on Wisconsin state and municipal obligations), but it shows 0 for line b), (Wisconsin state and municipal obligations exempt from both federal and Wisconsin tax), which is the "exempt" amount. How do I reduce the State and Municipal interest by the Wisconsin-specific interest that was earned?