A very confusing item arises:  See:

In addition to the limitation of Section 121 regarding depreciation recapture, as a part of the Housing Assistance Tax Act of 2008, Congress further limited the exclusion of capital gains for property that was converted from a rental to a primary residence. The new rules, enshrined in IRC Section 121(b)(4), stipulate that the capital gains exclusion is specifically available only for periods during which the property was actually used as a primary residence; any other time (since January 1st, 2009) that the property was not used as a primary residence is deemed “nonqualifying use”. Accordingly, to the extent gains are allocable to periods of nonqualifying use (gains are assumed to be pro-rata over the holding period), those gains are not eligible for the exclusion.