Investors & landlords

To complete sections A and B of Part II, you'll enter your closed contract positions separately, but you'll also include information about any unrealized gain on the offsetting position in section A column (g). The TurboTax input questions mirror the form boxes:

This way, any realized loss(es) can be deferred to the extent of the associated unrecognized / open straddle gain. And for closed positions, you'll need to enter the separate sale info (dates/basis/expenses) to properly calculate the gain or loss from that specific closed contract (leg) - rather than net or combine any offsetting transactions together. This also avoids any mix-up of tax treatment on closed contracts / sale transactions. 

This screen (below) is where you will complete the required Form 6781 Part II instruction "Attach a separate statement listing each straddle and its components." This is where you will identify the closed and open components from Part II / Part III as being legs of a specific straddle position:

IRS - Form 6781 Instructions

IRS - How To Report Gains and Losses (Form 6781)
 

Note: The software does not support all of the reporting required of dealers in regulated futures contracts. A dealer is someone who is licensed in securities, has an established place of business, and regularly purchases securities for resale to customers. Among other requirements, dealers must report gain or loss on the sale of regulated futures contracts as self-employment income on Schedule SE.