Group Filter not working in Custom Report

Content

We have developed a custom Report. The Data Model is a master detail query includes a main query and three child queries

Q_1 - Main

Q_2, Q_3, Q_4 are child queries linked to Q_1

In Q_1 we have a summary column for few columns from each of the child queries

TOT_A = Sum(Q2.Columnxx)

TOT_B = SUM(Q3.Columnyyy)

TOT_C = SUM(Q4.Columnzz)

We also have formula colmun in Q1 NET_TOTAL = TOT_A + TOT_B + TOT_C

We need to filter records where NET_TOTAL != 0 

Note that the values of all the summary columns , TOT_x and the NET_TOTAL are calculated correctly and displayed in the XML data.