Has anyone seen this behaviour with the World Clock (n900)?
Before going abroad I added the destination time zone in my world clock. When arriving there my local time automatically adjusted to that time zone so now both (added time and local time) were the same. Next I tried to add my home time zone to keep track of the time back home but it said that time zone is already added. I then removed the destination time I had added before the trip and tried different things but could not add my home time. As a workaround I added a time zone that was only 1 hour off for easier calculation...