5520 rebooting when desktop shutsdown

[Justdono]

I wonder if anyone here has seen the problem I am having and may be able to point me in the correct direction

My client has a number of Optiplex 755's that they have recently bought. These are connected into Mitell 5520 single mode phones. When the user shuts down there desktop the IP phone reboots as well and will not come back up onto the network. When the desktop is restarted the phone comes back up and runs correclty. This is only a problem with the new Optiplex 755 and only when connected to the Mitel single mode phones. We have disabled the management engine and thought this had solved the issue but it has returned.

Is there anything on the phone setup that I can possibly look at to get this resolved

 

[slapin]

Do you have any sort of dot1x authentication on ethernet switches or separate VLAN for voice and data?

It might be related to ethernet port settings of Optiplex. I had an issue when Optiplex cannot negotiate speed and duplex parameters. Try to change it to 100/full in Network adaptor properties if you have MS Windows OS.