And what you said above about Aaron reminds me of back when I used to do high voltage propulsion experiments. I'd always be on the look out for purple corona jets anywhere being the cause of the propulsion since I was looking for something more exotic. Once I found corona coming out of a section of thickly insulated wire, right through the rubber. If the voltage is high enough and/or the electric field is asymetric enough and there are tiny but not noticable holes then corona will go right through. Maybe Ghst's jar has some tiny tiny holes there through which some of the ionized air escapes unnoticed. Then when the radiant event happens, it just follows this ionized air out, like any other conductive path. Might be interesting if it's repeatable, to put a few layers of tape over the outside of the jar where it happens and see if it still happens. Just a guess based on experience.
-Steve