In SSRS 2008 I am trying to maintain a SUM of SUMs on a group using custom Code. The reason is that I have a table of data, grouped and returning SUMs of the data. I have a filter on the group to remove lines where group sums are zero. Everything works except I'm running into problems with the group totals - it should be summing the visible group totals but is instead summing the entire dataset. There's tons of articles about how to work around this, usually using custom code. I've made custom functions and variables to maintain a counter:

Public Dim GroupMedTotal as Integer
Public Dim GrandMedTotal as Integer

Public Function CalcMedTotal(ThisValue as Integer) as Integer
    GroupMedTotal = GroupMedTotal + ThisValue
    GrandMedTotal = GrandMedTotal + ThisValue
    Return ThisValue
End Function

Public Function ReturnMedSubtotal() as Integer
    Dim ThisValue as Integer = GroupMedTotal
    GroupMedTotal = 0
    Return ThisValue
End Function

Basically CalcMedTotal is fed a SUM of a group, and maintains a running total of that sum. Then in the group total line I output ReturnMedSubtotal which is supposed to give me the accumulated total and reset it for the next group. This actually works great, EXCEPT - it is resetting the GroupMedTotal value on each page break. I don't have page breaks explicitly set, it's just the natural break in the SSRS viewer. And if I export the results to Excel everything works and looks correctly.

If I output Code.GroupMedTotal on each group row, I see it count correctly, and then if a group spans multiple pages on the next page GroupMedTotal is reset and begins counting from zero again.

Any help in what's going on or how to work around this? Thanks!