It's possible some of the conductive paint got below the resistor and shorted it out .. I always let them dry overnight and then check conductivity with a meter ..
In the case of the conductive paint Ed is using, this is very important advice. I bought a tube and have been testing its characteristics:
1) It has a considerable resistance value when wet. I squeezed out a 1" line of paint roughly the diameter of the nozzle, the line measuring 5KΩ when wet.
2) It takes a while to fully cure. The test line was still pliable after 24 hours, although resistance had reduced to ~1KΩ.
3) It does not have zero resistance when dry, but in our application it may as well be 0Ω. The test line was 200Ω.
4) The cross-section of the test line played an important role in determining the final resistance value. Thinner = more resistance.
5) A test wheelset where I simply painted a line across the insulator went from ~500Ω to ~5Ω overnight. Prophetic. What I found especially interesting was while it scraped off easily, there was enough residue from the initial scraping-off to still be a virtual short. I had to hit it with a brass brush before it cleared. Probably should follow-up with alcohol and a toothbrush.
My edumaguess is the stuff is graphite powder in an acrylic medium. Resistors are made of some form of graphite mix. So what you have are grains of graphite touching each other in a suspension, the more grains touching, the lower the total resistance. A thin cross-section means fewer grains touching.
Bottom line for Ed's needing to summon the volunteer fire department was because there was enough resistance in the uncured dabs of paint to not anger the short-circuit gods. Like John said, the fun started apparently when one of the globs made its way under a resistor and dried to the point where it drew enough current for the light show.
