2002 Mazda Protege Door locks question

In the first year I never had this problem, but after I got an after-market car starter installed, it began doing something similar. I have a manual transmission, and the car starter is from Polar. In any case, if you unlock the car using the Polar car starter, then wait for five minutes, the car will automatically lock itself. If you press unlock on the car door itself, it will stay unlocked. The dealer said it was because the car starters for manuals had to activate the safety feature that was previously turned off. It's a pain, but I've simply learned to live with it, and never leave my keys in the car.