Mine does the same thing sometimes. It senses the door is closed, eventhough it is not, and if I don't shut it quick, the alarm goes off. I just live with it. I am guessing the door switch is sticking, or the sensor is going bad. The alarm should beep once when you initially arm it, and then again when all the doors are closed. If you arm it with the doors closed, it should beep twice. Pushing the blinking switch as far as I know just deactivates the alarm, which makes the car seem to only have keyless entry.
I don't think the dome light test will work because the dome light activates with the alarm/keyless entry feature. It stays on for a few seconds after the ignition is turned off (not part of the alarm, I think all Imprezas do that), and comes on when the car is disarmed with the doors closed and goes off once the car is armed. That is how mine works, and I have the dome light set (with the switch at the light) to come on when the doors open. Playing with the switch at the light wont tell you if the door switch is working anyway, it will tell you if the switch on the dome light is working, right? I think you would have to check the door switch with a test light. I'll have to look when I get home.
I have not brought it to the dealer because I think they'll just make things worse, and it is so intermitant, it will never happen in front of them.
[This message has been edited by paultg (edited July 03, 2000).]