Wrong amount in GR55 drill down report

[Anand86]

In GR55 report, we have created 2 columns with 2 types of budget version and created thrid column with sum of first 2 columns. 

Total amount is displaying correctly but when i click on drill down, displaying amount.

Example , column x with budget A = 10000and column Y with budget  B= 5000 and column Z with sum of column x and y = 15000

Sum amount 15000 is displaying in column z but in drill down report showing another amount 7000.

Can some one help us to resolve the issue

Thanks,

Anand