Why does TT calculate part year depreciation for real estate different from IRS rules? Shouldn't it be mid-month of month sold? TT calculates it based on prior month.

I sold rental real estate on 6/20/2017.  IRS indicates that depreciation for the year should be based on mid-month of month sold, so 6.5/12*annual depreciation.  TT is calculating it based on mid-month of the prior month, not the month sold, or 5.5/12*annual depreciation.  Why is this and is this correct?