If you are accessing your clients cpanel via whm, or the drop down list in your main account (ie not actually logging in with their username/password), it will show the last login as 127.0.0.1
When your clients go to : https://www.domain.com:2083 it is routed though software called stunnel. This means that the server can not identify the IP address and so replaces it with localhost 127.0.0.0
BTW, in the latest CURRENT/EDGE builds cPanel have changed all this and access to both cPanel and WHM is no longer through stunnel - they've coded their own SSL routines. So, one you're using those builds the IP will show up correctly whether using SSL or non-SSL access.
BTW, in the latest CURRENT/EDGE builds cPanel have changed all this and access to both cPanel and WHM is no longer through stunnel - they've coded their own SSL routines. So, one you're using those builds the IP will show up correctly whether using SSL or non-SSL access.