By default, when you’re viewing tickets in the list pane, the list of tickets matching the selected filter is updated in real time.

When a new ticket is created that matches the current filter, or a ticket is changed to match, it will appear in the list. When a ticket changes so that it no longer matches the current filter, it will disappear.

If you don’t want this to happen, you can disable real-time updating by clicking on the ‘refresh’ icon at the top right of the filter pane: