Why Grand Total are not equal to above sum(list items) in cubebrowser after reprocessing cube works fine ,why that happens?

I have got Problem with my production cube ,some one try to browse the cube with a Calculated measure  and slice with dimension then Grand totals are wrong then when i reprocess the cube it shows correct.what  could possible reasons for that,I want to simulate same issue in my test env.

Does anyone have  work around to avoid these kind of issues in Production?

Thanks

Praveen

ProM