I use GTD with RTM roughly as per this post:

http://blog.rememberthemilk.com/2008/05/guest-post-advanced-gtd-with-remember-the-milk/

I made one tweak in that I needed to make a central place where reminders or urgent tasks could catch my attention. So, I created a "Due" smartlist that simply searches "dueBefore:tomorrow". That worked beautifully for quite some time.

However, I like being able to use RTM for many kinds of lists, not just GTD. My wife and I share a household chores list, for instance, and since she doesn't use GTD it doesn't really fit the format of my system. So, I created a "Shared" list that I share with her and tag all the tasks that would normally belong in a given list with "l-[listName]". For instance, this list's items are tagged "l-chores". I also have a non-shared list "Errata" that also uses the "l-[listName]" format for my own lists (e.g. things to talk to the doctor about when I see him get tagged with "l-doctor" and stuck in that list).

Since I want due dates from some "l-[listName]" lists to show up in my "Due" list but otherwise want to ignore those extra lists, I had to add some parameters to my "Due" list's search. It now reads:

dueBefore:tomorrow and (tag:l-groceries or tag:l-borrowed or tag:l-library or tag:l-daily or not tagContains:l-)

Since I started doing this, though, each time I update a task in the "Due" list it vanishes. If I change its priority, change its name, change the tags it has that shouldn't affect the search, or otherwise modify it in some innocuous way, it just behaves as though it falls outside the parameters of the search. I then have to fix this by looking at a different list and then going back to my "Due" list, at which point it mysteriously reappears (with the modification I just gave it).

I'm pretty dumbfounded by this. Any thoughts or suggestions?