One tail light goes out when braking, not the bulb.

[Mental1]

I have a 2000 Legacy wagon, and the other night when my girlfriend was driving it I noticed that when she was braking the passenger side light in the hatch would shut off and its a slight bit dimmer when on normally. I changed the bulb today, same deal, it's on when I have all the lights but when I touch the brakes it shuts off completely. The bulb holder looks ok as far as corrosion and stuff goes. Could it be a grounding issue or some like that? Any ideas.

[chuckthefuk]

lets get the ball moving shall we:

0) Are you sure the bulbs are the right type?
1) Have you tried the bulb in a different socket (other side to confirm)
2) Have you taken a multimeter to the socket and tested + / - / other

-Chuck