List Join

[SeanP]

You could also use List.Combine and the List.Join as the method.

List.Combine + List.Join behave oddly - bug?

When List.Combine has 2 list input nodes (list1,list2) the combinator (in your case List.Join) should also have a corresponding number (2) of empty input nodes. I suspect your definition will work consistently (without you having to toggle +/-) if the List.Join node is as below. [20151216-5]