First, you can update to 1.0.9 - the release version. At least I
think you can. I'm using the non-Market version so I'm making some
assumptions about how the Market version updates work when you have a
beta installed.
The problem you're running into is that Display Off is an event, and
events are instantaneous, whereas other (non-event) contexts are
conditions that exist over a period of time. Because of the nature of
events, an exit task would run immediately following an enter task,
and not give you the results you're looking for. To do what you want,
you need to monitor the value of the built-in variable %SCREEN.
If you replace the Display Off context with the following:
Variable Value [Name: %SCREEN] [Op: Matches] [Value: off]
that should get you what you want.