Steps to reproduce

• Set your server timezone to Etc/UTC, for instance (that's what I have in my /etc/timezone)
• Set your local timezone to some timezone that is your localtime - x, where the result will end on the previous day (example: I did this test at 08:00am and set the timezone to Alaska i.e., my timezone minus 9:00 => 11:00PM of the previous day)
• Created a content type with a date fieldtype
• Created an object of the previous content type and set the date to "1938-01-01"
• Exit the date field. When I exit the date field, some validation is done and the date is updated to "1936-07-29". Every time I do that, the date changes to something different than the original value

Steps to reproduce (Yannick)

• Set your timezone in php.ini to America/Martinique
• Create a date in the platform UI, publish
• Display this date
• It is a day earlier than the entered date.