“Require all filters to be true for a task to show up” seems to be set by default, regardless if it is checked or not. In fact, if you check it, the check is not saved in the filter (but it is operating as a default filter).
To replicate: create task #1 with start and due dates, and task #2 with just a due date. Filter by both start and due date. With “Require all filters to be true…” unchecked, you will only see task #1 when you should see both.
Also a side note: checking “Require all filters to be true…” and “Include Tasks which don’t have a value set” should not be allowed, since they’re mutually exclusive. If all filters are required, then they have to have a value set.