Let's try to keep it civil. We know, "read the owner's manual." Or perhaps some of us feel that looking over your shoulder when changing lanes is common sense.
But "seriously" you ask? How about Tesla's marketing of Autopilot? Granted, the release notes for auto lane change indicate that we must first check to make sure that it is safe to merge - not specifically that we must ensure our blind spot is clear. Afterall, the car is loaded with sensors and cameras to do that for us, right? Oh, of course, most cameras are currently just for show and the sensors have limited capabilities.
Even after checking your blind spot and you face forward to engage the turn signal, a car could zoom into the space you just checked.
Point is, the system is really no better than changing lanes on our own. In fact, it's much more agressive (currently with 17.26.76) and less safe than doing it yourself. If this is how they described it at the time of sale or at delivery or at any other time for that matter, then it would be a non-issue and we would not be surprised by these near misses.
At this point, the car should be able to complete this task by checking the blind spot IMO. That fact that it still cannot do this with the auto lane change feature enabled is dangerous.