The partnership sale happens outside the partnership in that little area you are taken to when you click final.  You have to enter sale price of interest less the cost of the p'ship interest.

What you are seeing on the K1 is the sale of asset or assets in the partnership.  For instance the partnership owned an apartment bldg and sold it.  Those are the capital gain on the K1.  That does affect partnership basis but is irrelevant to sale of partnership.