Froxmox Ctrl Key Issue cccccccc

Hello

I work with Mint virtual machine in Proxmox 3.0

Whenever I click Ctrl key (Ctrl+C , Ctrl+X, Ctrl-P) in command prompt, it automatically inputs the characters such as cccccccc, xxxxxxxx, ppppppp

I tested different OS systems Ubuntu, Windows all the same.

Anyone has any idea?

Thank you