[KeithFK]

I guess that make sense to me because I've chosen to implement flags as an "on deck" kind of tag - I don't have any item that has both a due date and a flag.

I realize what you are saying about the way the system is functioning. My point is that I went to create a "Due items" perspective thinking that I wanted to see the items that have a due date assigned, not the ones that don't. I just hadn't done a very good job of recognizing how the software was thinking about the use of the filters to create a particular perspective. I'm getting a little better all the time, though!