ReportAggregators not including groups/stratifiers/etc. from both Reports

[JPercival]

Correct Behavior:

MeasureReport A {
   Group 1 = 8
   Group 2 = 3
}

+

MeasureReport B {
   Group 2 = 8
   Group 3 = 5
}

=

MeasureReport C {
   Group 1 = 8   <- Included from A
   Group 2 = 11  <- Included from A and B
   Group 3 = 5   <- Includes from B
}

Current Behavior:

Current Behavior:
MeasureReport A {
   Group 1 = 8
   Group 2 = 3
}

+

MeasureReport B {
   Group 2 = 8
   Group 3 = 5
}

=

MeasureReport C {
   Group 1 = 8   <- Included from A
   Group 2 = 11  <- Included from A and B
   Group 3 = MISSING! Wasn't present in A so it wasn't added! 
}