Browse Window question

In the browse window, specifically, the Due column: What does it mean when a due date is in parenthesis? I find it gives interesting behavior. For example, if I have a bunch of cards flagged “red”. Say 8 of them. Assume one of them has the due date in parenthesis, the other 7 don’t. (As far as I can figure, nothing else is different among the cards.)

If I put “flag:1” in the search box, all 8 shows up.
Suppose I create a filtered deck, with the search criteria for the deck to also be: flag:1

When I “rebuild” the deck, the deck only contains the 7 red cards with the due dates that are not in parenthesis. It does not include the 8th card. Why not? Why does the search work differently in a filtered deck than in the Browse window?

It means the card is buried or suspended.

Because buried and suspended cards cannot be included in filtered decks.