A few years ago, I was doing my usual WI-NR form for a client who did a two-week gig in Wisconsin every year. I was expecting him to owe a small amount, as he did every year, since this was 1099 work, ao any profit he made in the year pro-rated to WI, even if the WI trip was actually a loss leader.
Instead, the software took out the tax due, and reduced the liability to zero.
I looked at the form, and then the instructions, and thought I must've done something wrong, since neither one allowed the credit which eliminated the taxes due. So I overrode the software, took the credit out, and had my client pay the full tax liability.
WI refunded his money.
I called the tax office in Madison, and asked the nice lady if she could walk me through, and show me what I did wrong, so I wouldn't make the same mistake again. When we got to that line, she said, "those folks aren't eligible for that credit". I agreed. She went and got her boss, who had me walk through it again, and then he admitted it was an error in their equation. I asked if my clients would be billed; he said probably not (they weren't).
Now I realize I should've asked IF I WOULD BE ARRESTED FOR FINDING THE ERROR.