I had this issue too. I do scripted deployments and I solved this by doing the following (simplified):
1) Deploy the VM using New-VM
2) Power it on using Start-VM
3) Immediately after set the network adapter to be connected (this has to be done whilst powered on), using Get-VM -Name $computername | Get-NetworkAdapter | Set-NetworkAdapter -Connected:$true -StartConnected:$true
Hope this helps.