Olympus acknowledges E-M5 / 20mm banding and is working on fix
Olympus has acknowledged the banding that can appear in high ISO OM-D E-M5 images shot with the Panasonic 20mm F1.7 lens and says it is working on a fix. In the meantime, the only solution is to avoid high ISO settings when using that lens, for now. It says that it has tried 'every possible combination of body and lens,' and has not found the problem with other lenses.
'After checking every possible combination of a body and a lens, we found the phenomena only with this combination (OM-D, E-M5 coupled with the Panasonic 20mm pancake lens). We are continuing to study how we can eliminate this and we recommend for our customers using E-M5 with Panasonic 20mm pancake lens to keep a low ISO to avoid this problem for the time being.'