Right now you table cells grow and shrink with the content. When the content grows, so does the table cell. Since your dropdown is larger than the text the table reformats itself. This issue can easily be solved by setting a width and height on the table cell that changes. Here is your example, updated:
http://plnkr.co/edit/4xyoVxc7kn8dFWhNob4G?p=preview
By setting a width and height on the Event Name column the table no longer needs to reformat when the content changes.