I triggered same bug here with USB-cable from computer. It just keeps updating battery icon and led just blinks. I could restart this, but is there any other way to stop this.

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And i do not have usb-cable connected right now. It just keeps on going. Now about 1 hour.

When it comes to the Car charger, one will have to analyze the Car too.
Modern cars run some kind of "shut down routine", so after turning the engine of and pulling the key (pulling the card, leaving the car, whatever it takes) it can take up to half an hour until all electric devices (that should go offline) went offline. So, maybe the DC socket in the Car just keeps powered for another five minutes or so. My DC socket keeps powered till the battery is empty, wich is another option.

My N900 has multiple problems, one of which is charging. After fully charging it and unplugging the usb cable it says that it's still charging. It'll keep doing that until it runs flat!
If I have to turn it off for any reason I can't reboot it unless I have a charger plugged in (it just goes into a boot loop). That is a problem also since sometimes it won't recognise that a charger is plugged in (either the wall charger or the 2 car chargers)

I'm about ready to throw it at a wall!

How about using the 2 year warranty for that reboot loop problem?

I just got off the phone with Nokia. They want me to try a different battery. Just gotta find someone that has it.