Problem with the GF's car

[AMGala]

My GF has a 2005 Nissan Sentra 1.8SE. A couple days ago, when she turned the car off, pulled the key out, and her engine stayed on. She put the key back in, turned it to on, turned it to off again and pulled out the key. The engine still remained on. She put the key in one last time, turned it to on, put it in reverse and backed up a little, then put it in park and shut it off. This time the engine did shut off. Her car is completely stock except she has an automatic car starter. What do you think happened? Anyone else ever have this problem?

[nametakennow]

I'd start by checking that aftermarket starter. Seems to me that its installation could have messed with the ignition wiring.