In a DatetimeIndex using a non-static timezone over a time range that crosses the DST line, the time shifts around
For example:

> > > dr = pandas.date_range('03/06/2012 00:00', periods=25, freq='W-FRI', tz='US/Eastern')
> > > print dr
> > > <class 'pandas.tseries.index.DatetimeIndex'>
> > > [2012-03-09 00:00:00, ..., 2012-08-24 01:00:00]
> > > Length: 25, Freq: W-FRI, Timezone: US/Eastern

This is midnight at the start, but 1am at the end. Shouldn't it be midnight all along, regardless of DST?
