SortRecordList on RecordList of TWO structures


SortRecordList works fine for me on a RecordList of a single record definition, but I keep getting the "Failed to compare two elements in the array" message when I try it on a RecordList of mutiple structures.  Example:

ShipToItemList is a record list of two structures (WarehouseItem, ActionResult)

Trying to SortRecordList:
recordList: ToObject(ShipToItemList)
sortBy: "WarehouseItem.ItemNumber, WarehouseItem.SerialNumber"
isAscending: True

ItemNumber & SerialNumber are both attributes of the WarehouseItem structure.

Any help is greatly appreciated!