Hello bmc130,
The problem in case of PSX format is related to the following: the dense cloud is not loaded fully in the memory, so updating it performed partially, but in fly and the points are marked as deleted (allowing the Undo operation) but are actually kept in the cloud. Removing points completely after each point editing operation would mean re-writing of the dense cloud, that can take tens of minutes. I think we'll implement the option in the next update, allowing to remove the deleted points from the dense cloud completely by the user request.