Four to six weeks is a very long time for a pod to remain on the plant and not have any seeds in it. Usually if a plant is self-incompatible or if the ploidy of the pollen is different from that of the pod parent then the pod stays green and growing for less than two weeks and then dries up.
I don't have a reasonable explanation for the behaviour of this plant as it is not acting in a typical manner for any of the explanations.
However, if you would like to have more fans of exactly the same plant (for example, so that danger of the plant dying and being completely lost is reduced or so that you can share pieces of the plant with others) then Seedfork's suggestions are good.
