1993 misubishi 3000 GT

I have a 1993 Mitsubishi 3000GT with auto transmission.

A wired thing has happened several times.

when the battery is disconnected and then reconnected the car satrted on its own without the ignition key being in the swithch. this has happened a few times but not every time.

The engine of this car was replaced with an engine that came out of a 1994 30000GT with a manual transmission.

what could be the cause of this problem?

I would have to say there is a remote starter installed in the car that is causing that to happen.