If you are preparing a partnership return, why would you expect F.6781 to be generated for the Line 11C item from a pass-through K-1?  The income is taxable at the shareholder level and it will then be reported on F.6781 of the shareholder's return.

On the other hand, if you are preparing a 1040 the amount entered on Screen 20.1, under the section for Line 11 - Other, on the line for (11C) 1256 gain (loss) will flow correctly to F.6781.

Why is the Form 6781 available in the partnership return then?  If the Section 1256 transaction originated with the partnership?  So if it's just flowing through from another entity it just goes directly to the Schedule K-1 to flow to the shareholder then?  

And yes I'm preparing the partnership return.

Yes and Yes