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Sounds like the car thinks the key is in the ignition. This is from an 03 Matrix manual, but describes what the car does to try to keep folks from locking the keys in the car
4. Ignition Key Reminder Operation
∗ Operating door lock knob (Operation of door lock motors)
With the ignition key in the cylinder (Unlock warning SW on), when the door is opened and locked using door lock knob
(Door lock motor), the door is locked once but each door is unlocked soon by the function of the relay. As a result, the
current flows from TERMINAL 1 of the integration relay to TERMINALS (A) 1 and 3 to the door lock motors to
TERMINAL 2 of the relay to TERMINAL 9 to GROUND and unlocks all the doors.
∗ Operating door lock control SW or door key lock and unlock SW
With the ignition key in the cylinder (Unlock warning SW on), when the door is opened and locked using door lock
control SW or key SW, the door is locked once but each door is unlocked by the function of SW contained in motors,
and the signal is input to TERMINAL (A) 19 of the relay. According to this input signal, the current flows from TERMINAL
1 of the relay to TERMINALS (A) 1 and 3 to the door lock motors to TERMINAL 2 of the relay to TERMINAL 9 to
GROUND and unlocks all the doors.
∗ In case of key less lock
With the ignition the key in the cylinder (Unlock warning SW on), when the unlock function is disturbed for example
pushing the door lock knob etc., the door holds on lock condition. After closing the door, door courtesy SW inputs the
signal into TERMINAL 5 or 6 or (A) 13 of the integration relay. By this input signal, the relay works and current flows from
TERMINAL 1 of the relay to TERMINALS (A) 1 and 3 to the door lock motors to TERMINAL 2 of the relay to TERMINAL
9 to GROUND and unlocks all the doors
if that;s the case, then it could be the key sensing switch in the ignition lock or possibly an issue with the "integration relay", which is a plastic box on the under dash fuse block