Formula Results Inconsistent using math.spatial.Sum

Greetings,

I am working on creating a custom report in Vipr SRM 3.7 that SUMs the
metric "name==Capacity" for each Mapped and Masked LUN on a VNX array
and shows that summed value along with the LUN Count in the Parent report. I am
using this formula to Sum the LUN Capacity metrics, "math.spatial.Sum" on the child node and using that value in my Parent Table.

It seems the formula is not always consistent in its sumation. Sometimes I see the correct value in the report and other times not, (i am checking it manual against an export of all Masked and Mapped LUN capacities). 

Does anyone know why the formula values appear to be inconsistent? 

I can provide the report definition if that would help.

 

Thanks.