In Wisconsin, should I be paying state tax on foreign earned rental income?

Hello,

From Tax purposes, I am Wisconsin resident. For the 2015 and 2016 tax years, I have been reporting income from a rental property I own in India.

1. I didn't know this but I heard that even though the income is from a different country, I will have to pay state tax on it in Wisconsin. Is it true? (Because the income was not coming from Wisconsin, I was only including the rental income in the federal return but was reducing it from the taxable income in state return).

2. If the above is true, I am guessing I will have to file amendment to state tax return right - will there be any penalty for doing it so late?

3. Also, will I need to buy a separate product from TurboTax for this - I currently have TurboTax Deluxe 2016 installed on my PC, and will be purchasing 2017 version soon.

Thanks.