Possible bug with Listboxs

Is there a limitation with a multiple cascading list Box being populated from another multiple list Box? As mine is only showing the records from the first item selection instead of showing all records combined.

Referencing the pic: I would expect to see ‘Power’, ‘Road’, and ‘Watercourse’. If ‘LW-1 H-1 001’ and ‘LW-1 H-1 002’ are selected.

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