I'm trying to convert a UTC timestamp to one in the Spanish timezone.

```
>>> import datetime as dt
>>> import pytz
>>> today = dt.datetime.utcfromtimestamp(1573516800)
datetime.datetime(2019, 11, 12, 0, 0)

>>> today.replace(tzinfo=pytz.timezone('Europe/Madrid')).timestamp()
1573517700.0

>>> today.replace(tzinfo=pytz.timezone('Etc/GMT+1')).timestamp()
1573520400.0

```

I'm surprised that I get different results for `Europe/Madrid` and `Etc/GMT+1`. Why is this? Should `Europe/Madrid` be used differently, or it is possibly a bug?