This box is automatically calculated  and will switch to box 3  once you enter more than one property.

Unfortunately this solution doesn't work unless you say No to the first property being your principal residence.  That was the only way that tech support or I was able to get a check in box 3 of Schedule 3.  After an hour of trying, I was told that since I was paper filing the return to manually put an X in Box 3 when I printed the form.  We went through all of the questions, it was confirmed that I had inputted everything correctly, so the only reason left was a software glitch.