Custom date field format does not match the field date format when called via API

Creating a new custom date field I set the date format to be dd/mm/yyyy.

When retrieving the date via API the format changes to mm/dd/yyyy

Reproduction steps:

Go to demo site
Create new date custom fields for a relationship
Set date format to dd/mm/yyyy
Edit the data in any relationship
Call that relationship via API
Notice the date format is not the same as the one defined on the custom field