Why does clock app need time zone set?

[Robert Moskowitz]

Fedora24 and Xfce 4.12 (I think)

I just realized that the clock app needs the timezone manually entered.  
When I change system timezones (on the Amtrak Wolverine train to 
Chicago) the clock applet does not pick this up.

Entering the timezone in the applet gets the time to the proper zone.  I 
would think that the applet should be able to pick up the current system 
timezone and not make me change it within the applet.