Hi, thanks for taking a look.  Apologies, you're right.

I've attached an updated patch, the problem before was that it was possible
for a timer to be cancelled when there still existed proced buffers, which
broke proced-toggle-auto-update.

To reproduce, apply the patch and then type
>
>   M-x proced-toggle-auto-update RET
>
> The result is that the Proced display is not updated every 5 sec as
> expected, and the value of proced-auto-update-timer is nil.
>

I've tested this with the new patch, and it works for me.

Thanks, Laurence