Converting python datetime to timestamp and back in UTC still uses local timezone

Question

I'm working with a code that gives me utc timestamps and I want to convert them to appropriate datetimes. Unfortunately when I test simple cases with pytz the datetime has an added 6 hours (the CST offset to UTC). I need to keep timezone data correct because I am calculating difference between other timezones as well. Any ideas why and how to convert a utc timestamp to a utc datetime?

In [1]: import pytz

In [2]: from datetime import datetime

In [3]: import time

In [4]: datetime.fromtimestamp(time.mktime(datetime(7,1,1, tzinfo=pytz.UTC).timetuple()), tz=pytz.UTC)
Out[4]: datetime.datetime(2007, 1, 1, 6, 0, tzinfo=<UTC>)

In [5]: datetime.fromtimestamp(time.mktime(datetime(7,1,1).utctimetuple()), tz=pytz.UTC)
Out[5]: datetime.datetime(2007, 1, 1, 6, 0, tzinfo=<UTC>)

In [6]: datetime.fromtimestamp(time.mktime(datetime(7,1,1).utctimetuple()))
Out[6]: datetime.datetime(2007, 1, 1, 0, 0)