I've found a bug that I've been able to reproduce, so I'm going to describe it here in as much detail as possible.

I have a list called "Other" and a smart list called "Upcoming". And I have a task called "Get Milk" which has a note, and is task for the "Other" list, and also shows up in the smartlist "Upcoming".

If I login to RTM and go directly to the smartlist "Upcoming", it shows me the task "Get Milk", but it claims that this task has 0 notes. If I then click on the "Other" list, and view the task that way, it shows me the note. Then I can go back to the "Upcoming" smartlist and it will still show the note.

So.. to summarize.. notes for tasks in a smartlist do not appear unless the actual list that contains that task has been loaded already.