Is datetime.replace fundamentally broken?

Converting a timezone naive date time to a specific timezone gives a completely incorrect result.

import dateutil as du
import pytz    
du.parser.parse('2017-05-31T15:00:00').replace(tzinfo=pytz.timezone('Europe/London')).isoformat()

returns a one minute not one hour offset vs UTC

'2017-05-31T15:00:00-00:01'

I've seen a few datetime peculiarities before but this one is breathtaking.