Door locks me out

Once in awhile when I exit the car and leave the keys in it (like if I put gas in the car or run out for a second to mail something), the door automatically locked - locking me out! Naturally, I no longer leave the key in, but I some people think I'm making that up or I somehow locked it by mistake. Can you corroborate my problem so I can prove to them I didn't lock myself out through some fault of my own?
Thanks!