Thank you for the detailed answer.
I already drove AP1 for 4 years and with that hardware a roundabout was suicide.
But since i'm happy to get a Model 3 next week, I wanted to know how the progress is on that topic, but it seems it is not really better.
Where I live, they changed all traffic light crossroads to roundabouts. So this really matters, since Tesla talks about automatic driving on city streets later this year (text form the Tesla Model 3 Order Page):
"Coming later this year: Recognize and respond to traffic lights and stop signs. Automatic driving on city streets."
If they can't handle roundabouts till then, they better implement a safety net, like: A loud warning to take over and stopping the car before entering a roundabout, if no response from the driver!
The actual behavior, even what you described, would be very, very dangerous.
I'll hope for the best, but since they don't talk about roundabouts at Tesla, it probably is not on their radar.