Measure - Cumulative Totals

Question

I'm aiming to calculate a cumulative total for Income Accounts and cumulative periods.

However the formula below returns a number that is far different from I expect. Leaving the formula with the period filter returns all cumulative amounts which is fine.

However everything changes when I add the additional Account Filter. Any suggestions on what's not working/missing?

(edit --> removing the ALL in the AccountFilter VAR disables the cumulative impact and returns data for the period only).

Thanks

OS_PAF_INC_YTD:=
VAR AccountFilter = FILTER(ALL( 'GP Data'),'GP Data'[Rubric 1] ="01. Income")
VAR PeriodRange = FILTER(
        ALL (  'GP Data'),(  'GP Data'[Period] <=MAX('GP Data'[Period])
                     )
            )
RETURN 
    CALCULATE(
        -   [Sum of AMOUNT] ,
                PeriodRange,
                AccountFilter
            )