The calculation of the amount on line 19 of Form 6251 is quite convoluted, but I've seen no reason to believe that TurboTax is calculating it incorrectly and no expectation that any future update will change what you are seeing.
Passive activities are subject to loss limitations. If your losses are limited, increasing the reported loss will not change the amount of your loss allowed for the current year and, therefore, will not change the amount on line 19 of Form 6251. Instead, the amount of your passive loss carried forward is increased.
Because the allowed losses are calculated differently for regular purposes and for AMT purposes, the amount of unallowed losses carried forward for each of these purposes can be different. Even if you have sufficient passive gains to be able to use all of your passive losses in the current year, including those carried forward, in the current year, you could have a amount on line 19 of Form 6251 resulting from the differences in the unallowed losses for each purpose in the carried forward from prior years.
This leaves a limited range of net passive activity gains or losses in the current year where a change in gains or losses will result in a change in the amount on line 19 of Form 6251. Instead of increasing the amount of your current passive gains or current passive losses by only $1,000, try much large changes in either direction until you locate the range where the amount on line 19 of Form 6251 changes.
