I have graph that contains some graphitems with Y axis = Right and one summary [calculated] item with Y axis = Left, graph.get() can be found in graph.txt.
While graph is showed correctly on Screen (screen.png), graph preview is broken (preview.png or preview2.png, depends on "E1 summary" position in graphitem stack, top or bottom).

Also please note that there is no label on left Y axis on screen.png, I think it can somehow be related to ZBX-5841.