As the filtering does not happen in lua code it could be that unregistering an event via lua does not remove the filters on it.
Maybe event filters will only clear on reloadui and are designed to be used that way.
This is something you should ask to ZOs.
Did you try to just overwrite the existing one without unregistering it, does it keep the filter as well? (I assume this would be intended, where your usecase though would be "an error").
Just use another unique identifier for new registered events and do not re-use your before used myEvent1. I actually always counted +1 and registered the same event's filters this way, if there is no other unique eventName portion like the abilityId or some other Id available. But even then I think I counted a variable + 1 and added it as string via
Code:
eventName.."_"..counterVar
at the end to make sure I do not alter or re-register some already registered event + filter.