Comment 0 for bug 1674137

System: Host: GT70-2PE Kernel: 4.5.4-040504-generic x86_64 (64 bit gcc: 5.3.1)
           Desktop: Cinnamon 3.2.7 (Gtk 3.18.9) Distro: Linux Mint 18.1 Serena
Network: Card-1: Qualcomm Atheros Killer E220x Gigabit Ethernet Controller
           driver: alx port: d000 bus-ID: 03:00.0
           IF: enp3s0 state: up speed: 1000 Mbps duplex: full
           Card-2: Qualcomm Atheros AR9462 Wireless Network Adapter driver: ath9k bus-ID: 04:00.0
           IF: wlp4s0 state: up

After mint 18.1 upgrade had various issues.
After quite a few updates I started having issues with ifdown command.

I use a script with qemu to setup a bridge (br0) with tap0 and the default wired connection enp3s0. The script began giving off unknown interface errors.
Testing showed that the ifdown command changed behavior after the updates and now does this.
The behavior is not limited to scripting.
I changed the code from using ifdown to ifconfig enp3s0 down.
This fails also within the script but with no error.
It, however, works from a terminal just fine.
I switched to using the ip command i.e. ip link set enp3s0 down.
Same result, the interface does not go down, but no error.
After the script is run and windows 7 boots in qemu I have to open a terminal and run the commands manually:
>ifconfig enp3s0 down
>ifconfig emp3s0 0.0.0.0 promisc up

Then all is well.
These commands will not run from within a script.
The script is run as such:
>sudo ./up.sh tap0

It creates br0 and tap0 and adds enp3s0 and tap0 to the bridge.

The fact that ifdown no longer recognizes any interfaces seems to point to a change in net-tools that has broken something.