While the IRS allows you to sell one time w/o a capital gains tax on the appreciated value less purchase price and improvements. Wisconsin goes CA & NJ one better and charges the capital gain if you don't reinvest in the state within six months.
I had a friend from Ohio who lived in Racine and when he retired sold his house there and moved back to Zanesville. The state went after him for the capital gain, he fought it all the way up to the Wisconsin Supreme Court and lost. He finally paid.
Regards,
GtG
Ouch! Exit taxes are just Un-American.