Further, setting the last stop depth to 3m/10ft does not prevent the diver from performing the last stop at 6m/20 ft (or any other depth such as 4.5m/15ft for that matter). There is no extra penalty imposed for staying at the deeper depth. However, if you stay at the deeper depth, tissue updating is always based on the actual depth, so off-gassing will be slower, and the predicted Stop Time and TTS will countdown slower than real-time. The predicated times are assuming that the diver will be following the prescribed stop depth schedule.
Yes, that's the point.. if you want to follow the computer literally and having the prediction matching, you will ascend to 3 meters, and then (if it's enabled) you should perform your safety stop a 5 meters. We know you can perform your last deco at 6m with no penalty, as opposite you can still at 3m do to your safety stop (it's right at the edge of the safety depth limit), but still odd to visualize a safety stop at a deeper level than your deco... so yeah, if it can be selected with the next patch, it will be great.