Re: Should `cancel-timer' use `delete' instead of `delq'?

[Richard Stallman]

    If you should happen to evaluate `run-with-idle-timer' more than once using
    the same arguments, then a different timer (vector) would be created and run
    for each evaluation. If you assigned the result of `run-with-idle-timer' to
    a variable (setq or defvar), then passing that variable to `cancel-timer'
    would cancel only the timer that was last created with those arguments to
    `run-with-idle-timer' (and assigned to the variable).

    I don't know - is that a feature or not?

It is the way Lisp works.  If you want to remember more than one
object, and operate on them, you can keep them in a list.