It happens. AA has autoreaccom, so if it's showing lets say:

LAS-CLT flight isnt getting into CLT until 9pm, 50 min late, and the CLT- MSY flight leaves at 905pm, it can rebook you for the next available routing to MSY and put your earlier CLT-MSY in NO status. Thus, your ticket on that nights CLT-MSY is gone, and possibly taken by someone else.

In fact, in the most recent nationwide time change, there was a glitch where the computer time was off, and it was rebooking people off flights that were there well before and in time.