The projects and resources are actually using the same "Standard" MS Project calendar. But the problem seems to arise from the fact that the subtasks are set to manually scheduled mode, while the task rows are automatically scheduled. Manually scheduled rows automatically include a start date of Sunday as a working day since you manually set that date (even though its not on the calendar), but the parent "automatic scheduled" row that changes to match the new start date does NOT include Sunday as a working day because it's not on the calendar.