Comment 4 for bug 405195

Fixed in Debian and thereby also in >=Zesty.
But the fix there is to move to the new systemd units. Which can't be directly SRU'ed.

OTOH even the sysV init is just like that for quite a while.
        if [ -z "$2" -o "$2" = "zebra" ]; then
          echo "Removing all routes made by zebra."
          ip route flush proto zebra
        fi

That is more or less the change that was suggested.
That is actually in since 0.99.22.1-2 which even Trusty is newer.
So I'd think it was only forgotten to close the bug here.