03 accord

Just bought my son his first car. 03 accord v6 automatic. The only issue with the car is you have to put in 1st when starting out. Then put in drive and it shifts fine. Then at a stop it goes back into neutral. Put it in 1st and it’s all good again. Ideas of what it could be. I am thinking a solenoid issue. Since it shifts fine and doesn’t slip if you put it in first before taking off.