Lumix 20mm on Oly EPL5, Problems?

Yeah, the size of the 20mm, and the near $150 price difference is more then enough for me to justify choosing it over the 17 and just living with the extra 5-6mm to the focal length.  I did hear that not all sensors showed the banding so I will be testing the mess out of this combo before I make the final decision.  If banding occurs, it goes back, and I will wait for the 17mm.  I'm still in wonder how one lens can produce banding and another can not.