Can you provide a sample workbook so that it will be easier to have a look you question?
Was just prepping this sample workbook this morning, and noticed that indeed I was doing something really silly... and I've solved it.
I was replacing the "TOTAL" with "WINDOW_SUM", but only dragging the pill back to the rows shelf. I wasn't replacing the text label, which was then still working off of the default "TOTAL" function created by the table calc... feel very silly, but this was immediately clear after taking a break and coming back to it this morning.
Thanks for responding though! I am sure you would have spotted it immediately