The element on the diagram showed a locked so double-clicking on it would not
get in edit control mode when an element or diagram is associated to it.
However, after re-starting ide or close and reopen uml project, the lock is gone
from the element on the diagram so double-clicking on the element no longer
brings up the dialog but get in edit control mode. 

Repro steps:
- create a uml project
- create 2 activity diagrams
- create and name a couple of invocation elements on each diagram
- from one of the element on the 1st diagram, right click and select "Associate
With..." from the context menu
- from the "Associate" dialog, enter a string that matches the 2nd diagram name
and click on Find
- from the result, select the 2nd diagram from the Search Result table
- check the "Automatically Set the Navigate on Double-Click Option" checkbox
- click on "Associate" button
- close the dialog. a lock is displayed on the upper-right corner of the element
on the diagram
- save and closed the diagram
- re-open the diagram. the lock on the element is no longer displayed.