@Aaron

OK, your last video showing measurements of capacitor potential with both inverter and capacitor disconnected did clarify things considerably. I didn't realize that capacitor after a discharge through a primary retained any kind of charge. I am now more inclined to agree with you on the comparison with Gray tube.

Could you please do a simple experiment- just reverse polarity of the whole system and compare results with the ones you tried already. By reversing the polarity of the system I mean connecting common ground to (+) of the inverter output instead to (-) as well as reversing the polarity of the high voltage diode. That should provide you with a positive high voltage pulse striking on positive retained charge on the capacitor. Positive charge striking on positive charge sometimes behave differently then negative charge striking on negative charge.