Oh BIS, what have you done this time???
If I create a trigger on a client assuming it will exist only on my client, I would be so wrong. The trrigger becomes global object just like createVehicle object. It will only trigger condition and statements will be local to the client even if I change trigger locality with set owner, however if I log out the trigger will automatically become local to the server just like any other MP object and will remain as such until the end. Any client that joins will be forced to synchronise and will also contain this trigger object.
This is nothing when you think of the implications. If you have 10 triggers set per client, after 20 people join, the server will have to sync 200 triggers, after 10 people leave and rejoin there will be 300 triggers. Run server for an hour with people constantly joining and leaving and... give yourself a facepalm :)