I encountered the same problem now with Linux Mint 15. I have a usb cable bound swiss-german keyboard (logitech).
Changing /etc/default/keyboard as mentioned above helped me too.
Additionally I observed the same issue now with Ubuntu 13.04 (BUT not with 12.10). So I guess it's not a Mint specific issue.
I encountered the same problem now with Linux Mint 15.
I have a usb cable bound swiss-german keyboard (logitech).
Changing /etc/default/ keyboard as mentioned above helped me too.
Additionally I observed the same issue now with Ubuntu 13.04 (BUT not with 12.10).
So I guess it's not a Mint specific issue.