In the GUI, if I Ctrl-Click a project and select 'Completed', the project icon displays a green tick, and the project actions are not set to 'Done'.

If, however, in Applescript I set the Completed property of a project to True, as in:

set completed of SomeProject to true

the effects are different. The project icon acquires no green tick, but all of the actions under the project, to the nth degree of nesting, are set to 'Done'.

I think I prefer the GUI effect. It is by design that the Applescript effects of setting completed to True are different ?