Isn't the whole point of even having an alias for it to be unique to that event and only that event.
Yes I know there is an option to make it auto increment aliases as you make new events but why is there nothing to stop you accidentally changing it to one that is already being used, considering having 2 events with the same aliases causes it to be confused and start registering people against the wrong event so they are presuming its unique without making it unique. Considering forcing them to be unique is what Joomla does with all its aliases is there a reason why this component is not following the same standard.
