That means the policy would someday end up providing more in tax credit than taxes owed. Wisconsin's income tax rate doesn't hit the 7.65 percent maximum level until a tax filer reaches $300,000 in income.

At $300,000, there would be enough credit left over to shelter another $39,400 in outside income. The amount of credit exceeds state taxes due until a filer reaches $1.5 million in income.

"I have a strong suspicion they did not realize how many of those credits were going to pass through individual tax returns," Harris — who has been critical of the credit since it passed with the last biennial budget — said.

Because the tax credit still has more phases to come, Harris said "the taxes will continue to be cut, and it’s not clear if there will be sufficient growth in the economy to offset that."

Harris said he doesn't think Republicans have been responsible with their budgeting.

After the revenue numbers were released, Republican lawmakers heralded an increase in sales tax revenue from the previous year, although the amount brought in was still lower than projected.