todo-prefix default value has odd diary interpretation

["Denis Bueno" <dbueno@gmail.com>]

[Crossposting because this is half request-for-help and half bug-report.]

I recently started using diary and todo-mode. I use the following
customisations to have emacs display appoinments as they occur:

;; Remind me about diary entries.
(add-hook 'diary-display-hook 'appt-make-list)
;; Also display the diary when I do M-x diary.
(add-hook 'diary-display-hook 'fancy-diary-display)
;; Enable #include in diary.
(add-hook 'list-diary-entries-hook 'include-other-diary-files)

As suggested in todo-mode.el in the emacs trunk, I enable diary
includes so that my todos show up when I'm reading my diary for the
day. This behavior is useful. However, I find one thing odd:

If I add a todo to some category at (say) 09:00 on Tuesday, then when
I read my diary wednesday morning, I get an "appointment" at 09:00
whose text is the text of the todo. This doesn't make any sense,
because the time at which I added the todo has nothing (necessarily)
to do with any kind of "deadline" for that todo (I put the deadline in
scare quotes because todo-mode appears to have no concept of deadlines
for todos).

So, first: is there a way to set a deadline for a todo, such that
emacs will display an appointment at the time of the deadline for the
todo?

Second: should this behavior be changed so that the time of entering
the todo should not be considered an appointment time?

Please let me know if I'm confused, or if you agree with my confusion.

Thanks.

-Denis