I realized the numbers are different when you check the box vs putting a negative number on line 8.

Taxable Society Security Benefit calculation is different.  If you check the box the Unemployment Exclusion doesn't count for SS Benefit calculation, it is treated like Excluded Interest Income.

If you force a negative number on line 8, SS Benefit calculation will just take the entire line 8 without adding the exclusion back in.

Interesting.

Update:  Student Loan Interest deduction is also different.

Man... just use the box.