Grand Total for Original Duration and Remaining Duration

 Hi, I have a smiple Group and Sort based on a one Global Activity Code for "Systems" and checked the box for "Show Grand Totals", NO filters.

I added these columns "Original Duration" and "Remaining Duration", The "Grand-Total" for both is not correct! what is the issue?

Thank you

I think I figured what it's doing, it is just summarizing the duration from the very start to the very end of all tasks. is there any way I can sum the duration of these tasks any way, just by normal +

Thank you