yes, I installed Linux version 8.2 and all goes well, but when I installed Linux-image-amd64 from debian backport all is wrong, exactly debian packages linux-image-amd64 version 4.2+68~bpo8+2, the problem as like as Proxmox 4.0 or 4.1
ok, so it's seem a kernel bug.
can you try old proxmox 3.19 and 4.1 kernel ?
http://download.proxmox.com/debian/...a1/pve-kernel-3.19.8-1-pve_3.19.8-3_amd64.deb
http://download.proxmox.com/debian/...eta1/pve-kernel-4.1.3-1-pve_4.1.3-7_amd64.deb
it could help to see when this bug appear.