Again partnership taxation is super complicated. There probably isn't a bug in TT, but there isn't a lot of hand-holding because of the complexity. TT will work if you know what you are doing and if not you're probably better off seeking professional advice.
I think (but you should verify) that TT is asking about outside basis for the disposition of your partnership interest. Inside basis is relevant to the partnership when it disposes of assets.
You are right that TT's K-1 Section A/B page 3/4 "passive activity adjustment to income or loss" is critical to understanding what is going on. That worksheet shows where the various items of income/loss from the K-1 is flowing, if any is suspended because of the passive activity loss rules, and if some was PAL disallowed in prior years but is now allowed during the year of the total taxable disposition of your partnership interest.
When you enter the info relating to the disposition the math should work out such that it is picking up only so much gain/loss as is not indicated elsewhere. (E.g. the "extra" gain will showup on line 6d and flow to schedule D. That might be zero because your adjust basis was reduced to zero by distributions that show up elsewhere in Section A/B with matching zero proceeds.
If all of your proceeds are already accounted for in the other lines on Section A/B, then they probably adjusted to zero. No proceeds and no "extra gain."
But that doesn't happen all the time with all partnerships. Sometimes you get cash at the end and it doesn't show up as taxed on the other Section A/B lines. Then TT figures the gain and puts in in the right place. It sounds like you had no proceeds from the sale that were not taxed on their own right.
But this is so super complex, so you should verify this all with your own research and/or professional advice.
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