Print out the tax return before checking the box. 

Print out the tax return after checking the box.

What changes?  What is resulting in higher tax?  I first guess it affected some tax credits, but maybe it could affect something else.

Did you try clicking the yellow question mark on the toolbar when your cursor is in the box? Sometimes theyve got good tidbits of info in there about a particular line or box.

The description implies it meets some sort of exception so it is not passive income.