On Mon, 2017-12-18 at 15:32 +0100, Didier Kryn wrote:
>      I've just done apt-get source ifupdown.
>
>      The source contains two patches:
> 0001-Fix-a-crash-when-multiple-interfaces-are-specified-f.patch
> 0001-Unconditionally-ifup-hotplug-interfaces
>
>      So it seems things are well done and it is enough to remove the 
> second patch (attached).
> However, looking all over the package source, including debian/rules, I 
> can't find where the  patches are applied.

The patch is against the file /etc/init.d/networking, see the patch.