Repro steps:
1. Create a 20 day task
2. Create 5 consecutive days of holidays in the middle of that task.
3. Turn on 'show holidays' - observe task is 20 days. Good, assuming people are working through the holidays.
4. Turn off 'show holidays' - observe task is 15 days. Bad, assuming people are not working through the holidays.

Expected: the task is 20 days regardless of whether or not holidays are shown.

As an aside, it would be nice to separate the display of holidays and whether or not people work on holidays.