this is one of those "why didn't I know that?" stupid little things...
this caught me off guard as I was traveling, I went to a city that I knew was under the next timezone, so I adjusted my cellphone, but the time didn't change... I got confused for a little bit, then started changing to other timezones just to realize this fact
after that I verified the same behavior on my PC, if you still don't believe it you can try right now, switch your pc to different timezones, and you'll see the time changing unexpectedly
e.g. the actual time is the same at
(GMT-07:00) Mountain Time (US & Canada) and
(GMT-06:00) Central America
I know of at least one application where this actually causes a problem...