Little leaf disease

Anyone familiar with diseases associated with phytoplasma, a rather insiduous bacterial infection?
Little leaf disease and witches broom are symptoms of phytoplasma, although these also have other causes. I can find almost nothing on the disease in Buddleja, but I think I have an affected plant.
In the attached photos, the infected shoot has tiny, willow-like foliage and is congested in comparison to the normal shoot. This is from B.davidii Nanho Blue, where the change is most dramatic, but I have seen a similar problem is other cultivars. Do you think this is phytoplasma or is there another explanation?