I'm still having this issue, posted some pics in another thread on S.A. pollination. The flowers seem to be making it unaffected, and I have been pinching off the affected leaves. The condition hasn't responded to any fungal sprays, hort oil, or holistic treatment (focusing more on the trees general health with better nutrient application, paying more attention to watering, pest management etc.)...
I'm also fairly convinced it's not sunburn...
it starts at the leaf edges and presents like being burnt black to a crisp and gradually consumes the whole leaf...
I'd love to figure out what this is and how to treat it.