Once a task calendar is associated with the task by explicitly selecting a calendar, the task calendar overrides any other calendar(s), including the default enterprise calendar (if the task has no assignees) or the resource calendar(s) associated with any assigned resources.
To "reset" the calendar behavior for the task, select the Resource Calendar(s) option from the calendars list.
When you select this, valid dates for task work are determined based on the resource calendar(s) if there are assignees, or the default workweek calendar if there are no assignees.
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