While switching dates via datepicker, I noticed the date parameter is not equal between the two date parameters:

• changing datepicker to 2017-09-18:
  piwik/index.php?module=CoreHome&action=index&idSite=1&period=day&date=yesterday#?idSite=1&period=day&date=2017-09-18

• Changing datepicker to 2017-09-21:
  piwik/index.php?module=CoreHome&action=index&idSite=1&period=day&date=yesterday#?idSite=1&period=day&date=2017-09-21

As you can see, only the second date parameter gets changed while selecting another date.

Switching over to a week of data shows the following:
piwik/index.php?module=CoreHome&action=index&idSite=1&period=day&date=yesterday#?idSite=1&period=week&date=2017-09-07