I would suggest you can try different host to verify this issue is on client side or host side.
Also, search such topic over the Internet with the information about your VNC client and server.
VNC is just a abbreviation of virtual network computing but not specific software. There are lots of VNC server/client around the world, so we cannot make sure what kind of server and client you are using.
Also, what kind of keyboard layout is on your host? What kind of layout did you set on your nano?