And now that our first newborn has arrived I'm running into the same issue where the doors automatically lock when walking around the car to get something from the other side. At the very least, this problem could be solved with updated firmware/programming from Mazda but I doubt they care enough to spend time/money/resources addressing it.
I'm not sure how this can be. The transmitter in the door handle has a very short range--as do all proximity key systems. If you step a few feet away from the door handle, and have someone else press the lock request button, the car won't unlock--try this with any car with a proximity key. So when you walk away, and the key is no longer detected within that 2-3 foot range, the car locks. The car doesn't know you are walking around the other side to put your kid in the car--all it knows is that the key fob is no longer detected. The only solution is to turn off the auto lock feature.