Oops, I see that I forgot to elide a clause from the conditional that assembles the list of tasks!
Code:
set TaskList to TaskList & (tasks of currentContext where blocked is false and flagged is true and completed is false)
should instead be:
Code:
set TaskList to TaskList & (tasks of currentContext where blocked is false and completed is false)
Otherwise, you'd only get tasks in the desired context which happened to be flagged. As it turns out, for the context I used as my test case, they were...
Don't forget that you have to edit the property contextIfNoSelection to have the name of your desired context (sounds like "iCal" is the right value).