DAX: Running Total in Pivot Table (Works until filtered)

I've always had this issue with my Running Total formula - works only when there are NO other filters

I should say - after you've set up the report - you can't apply additional filters 

I've solved this by creating a separate tab for the Running Totals reports where no filters/slicers exist that let you modify the data.

We should be lucky enough that Marco Russo sees this post and answers us (I use the formula from his book)

How many tables do you have in your data model?

I bet your filter comes from a different table than where the measure is - because sometimes if the filter is from the same table the formula works fine? So when you apply the filter from a different table it doesn't filter the table with the measure the way you want it too and consequently produces the wrong result.