The current implementation of the double-click task edit feature is not an intuitive user interface action.
Also, there is absolutely no need to automatically edit the properties of the task model when you click on GanttColumns.
Give the developer independent control over the behavior of the edit event.
1. Implement support for the "IsEnabled" task model property that disables editing the property for the GanttColumn and double-clicking on the Timeline panel
2. Implement support for the "Edit" command for the GanttCommandButton