Management Reporting: Function for Trailing Twelve Months (using Range & Period Offset NOT working)

Summary:

I have a TTM (trailing twelve month) P&L report that works perfectly when i pick any period except DECEMBER. When I pick December, it gives me some strange output (but not the preceding twelve months). If I pick ANY period other than December with the below criteria the report will work just FINE. I can't figure this out.

Her is my current selection for 'Period' dimension:

*FROM Member: PeriodOffset of CurrentPOV - 1 for periods under YearTotal

*TO Member: PeriodOffset of CurrentPOV - 11 for periods under YearTotal

Please note: when I set the "*TO Member" to be offset by -12 the report works, but gives me one extra period I don't need to see (i.e. report shows 13 total periods. All I need is the current period and the preceding 11.