Get your taxes done using TurboTax

Yes, it seems contradictory, until you read line 20 completely. 

When you have unrecaptured 1250 gains, the total shows on line 19 of Schedule D. Line 20 refers to lines 18 and 19, asking if both are blank. When you answer No, you are directed to skip lines 21 and 22 and use the Schedule D worksheet to calculate your tax.