When changing the timezone in php.ini file to the west, it affects displaying the date in the front-office (the date changes to the day before). The user would expect the date to stay the same no matter what if he uses the Date Field Type.
The issue only happens when displaying the value in the front-office. Back-offices on tested versions (1.7.7, 1.13.2, 2.1.0) seem unaffected.

Steps to reproduce

1. Create new eZ Platform installation.
2. Create a Content Type with a Date Field Definition.
3. Create a Content Object of this Content Type, giving it a date value, and publish it.
4. Navigate to this Content Object in the front-office. Confirm that it displays correct date.
5. Open your php.ini, and edit the entry, for instance:

   date.timezone = "America/Puerto_Rico"
   

   instead of whichever entry value you have there already.

6. Navigate to this Content Object in the front-office. It will now display the incorrect date (the date from the day before)