Interesting Mike,
I have seen a similar effect with green indicator lamps. These are not the Neon ones but got a different gas in them, probably Argon.
If they were turned of a glow remained for a while,
then,
when they were dark, and once in a while they flickered back on very briefly but not at a regular rate.
These indicator lamps did not have any electronics in them , only a 68 k Ohms resistor.
