Comment 1 for bug 989577

I have found a solution of the described problem:

I had have this additional entries in my /etc/sudoers:

# Allow proxy environment variables to pass through
Defaults env_keep="no_proxy NO_PROXY"
Defaults env_keep+="all_proxy ALL_PROXY"
Defaults env_keep+="http_proxy HTTP_PROXY"
Defaults env_keep+="https_proxy HTTPS_PROXY"
Defaults env_keep+="ftp_proxy FTP_PROXY"

After deleting this two entries

Defaults env_keep="no_proxy NO_PROXY"
Defaults env_keep+="all_proxy ALL_PROXY"

kdesudo works again.

Note, the environment variables NO_PROXY ans ALL_PROXY are not defined for my normal users, so perhaps this was the reason, why kdesudo fails in Kubuntu 12.04.