Deductions & credits

I went back to look at Other Tax Situation and looked at Underpayment Penalties and lo and behold, apply refund to next year was checked.  However, when I try to change it to Give me the full refund, it doesn't let me make that change.  When I come back to that selection, the apply refund to next year is still checked even though I changed my selection.   

 

The other question that comes to mind is how much of the refund does TurboTax calculate to be withheld and applied to next year?