As a test I simply hooked up a 12v battery to my Ignition Coil and then hook the Ignition coil to a CFL. It will light the CFL extremely bright for a second and then go out. If I tap the negative connection to the negative post of my battery it will flicker.
I think your experiment similar to mine. Although I use 1.5V battery:http://www.youtube.com/watch?v=73VS6VeockY
It is caused by coil collapse current. When car coil primary get charged by the battery there is some change in the current pasisng the coil. This will propagate to secondary but may not be enough to light up the CFL.
But when you disconnect the power, the charged current stored in the car coil primary will collapse as fast as coil resistance allowed and generate high voltage. This high voltage then propagate to secondary and light up the CFL.
This is why you can only light up the CFL for a moment. Notice that you can get bright light only at power disconnect.
To do this continuously you need self oscillating relay or Joule Thief circuit or transistor driven by timer. I prefer the later one with 10% up time, currently running more than a month at about 6 hour a day without failing or heating up, not for lighting CFL though, just for energizing my drink water or occasionally charging some battery.
Relay (IRO) give most power but the waste spark make it hard to increase output. Transistor is less efficient by allow much powerfull output.
This effect should not be called BEMF, instead it should be called coil collapse current according to Peter Lindemann.