I too have seen this issue. But most of them with Windows. Never had the issue with Windows 2008/2012. But..... the issue is not consistent. With Windows 7 the shutdown does not occur if the Windows 7 VM had been running for quite long time without any restart. Even if i shutdown manually from console, it takes long time to shutdown, occationally just freezes. Same Windows 7 VM if i initiate shut down from Proxmox GUI shutdown button after running just for half an hour or so, it shuts down just fine. I always thought it is because of whatever was Windows 7 doing causing this time out error and nothing has to do with Proxmox itself. Only two or three times i saw the error with Linux VM. Again, they were somewhat loaded and had been running for over 4 months without any reboot.
yes of course. pressing it a 2nd time gave a log entry for it - curiously the 2nd attempt had the fail msg come up first while the first attempt was still spinning. eventually they both went to 'fail' (though the first one
might have only failed once I killed it from the cmd line actually..)
Basically there's no web-way to kill it, Im guessing.