My client's taxable income is lower than his capital gains on form 8995A.

So it did not calculate the QBI deduction.

For example - in general terms: 

Taxable income including capital gains = 800000

Taxable income excluding capital gains = 40000 (due to large stock donation of $250K)

Capital gains from the house + others were 900000

Just to see what the software would do I overrode the capital gains and put zero.  

Then it gave him the QBI deduction.

Just wondering about the reasoning behind this as per tax code.