I checked the 5.0.10 source code, and it's a bug. It seems to be fixed in 5.0.11 and 5.0.12.
You can upgrade, or fix it easily by
editing:
/opt/zimbra/jetty/webapps/service/zimlet/com_zimbra_url/url.
js
and find this line:
Code:
escapedUrl = "http://" + escapedUrl + "/";
and change it to:
Code:
escapedUrl = "http://" + escapedUrl;
and restart the server.
Good luck