OK , I think I maybe understand what's up. Maybe.
When I see my refund go down after splitting box 21 into boxes 52 and 53, I think it's going down to the correct refund! Cause when I see the Income Summary page, I see that 50% of box 21 is showing as "taxable capital gains". Before I put any values into boxes 52 and 53, my "taxable capital gains" was zero!
