I dug a little deeper now and this is what I found. I had a deeper look at systemd service files and subsequently called openvswitch scripts in /usr/share/openvswitch/scripts. I don't know if its upstream or patched by DEBIAN by AFAICT it seems to me that it is intended behaviour to keep OVS interfaces up during update/restart (no ifdown/ifup intended), right?
But then with v2.15.0 packages probably the actual start_daemon of ovs-vswitchd in do_start_forwarding() in scripts/ovs-ctl does seem to bring OVS interfaces down (as opposed to earlier versions?). And then there is nothing in place to bring those interfaces back up. I assume this is also why a subsequent manual ifdown/ifup fixes networking. Can anybody confirm that assumption of mine, please?
