When a file in an EVENT is edited and a new version is created then this new file will be added to the
EVENT if the EVENT is based on Date-range, Folder or Category.
When this happens for a file in an EVENT based on Selection this will not happen.
I think that in this case the newly created file, being a version of a member, should also become a member of the EVENT.
Is there a reason why EVENT membership should/could not automatically propagate from Master to Version
in all cases?
There is no propagation attribute for events.
If this is an issue for you, I recommend you use date-based, folder-based or category based event types for files for which you intend to later add copies or versions.
This would automatically "propagate" events.
Feel free to add a feature request so we'll see how many other users consider this a problem or something that should be added.