Only renders 1 item when itemHeight not explicitly set and complex components in use

[ghenry22]

If [itemHeight] is not set and the item is a basic DIV then the list renders as expected.

If [itemHeight] is not set and the item is a complex component then the list renders only a single item (that 1 item renders perfectly fine)

If [itemHeight] is set then both scenarios work.

Proposed Solutions

1. Ideally auto determine height of items even when complex components are in use.
2. Update the docs to explain this behaviour and make the requirement to set [itemHeight] clear.