CentOS 7 installed from the OpenVZ repo can cause a problem using the Console built into Proxmox. When you launch the console, you will see two prompts for username and if you try to login the two shells will conflict and prevent you from using this feature. The problem is caused by the switch from inittab to systemd. Luckily, the fix is very easy.
In order to stop the two login prompts from conflicting, you need to disable the getty that comes enabled by default. Using either SSH directly to the VM or by accessing via
vzctl enter <vmid> from the host run the following commands:
systemctl stop getty\\@tty1.service systemctl disable getty\\@tty1.service
Once those have been run, you should be set to use the Console feature of Proxmox.