the safety on my m40 will occasionally engage while racking the slide during dry-firing. it hasn't happened while at the range, so i assume its only when there isnt a round in the chamber.
personally, i keep my m40 and m9 with the safety engaged. but thats for at home, as i haven't begun carrying yet. i think having a good holster would set my mind at ease and i wouldnt engage the safety while its concealed.