Sharepoint App (iOS) date not accepted when adding list item

So basically. We have a list with a date field.

When we log in from the iOS app and try to add a new item with a date we get an error message.

It tells us that the date should be in the format "2016-12-24" whereas the datepicker in the Sharepoint app adds it as "24 Dec. 2016". If we add an item without the date, everything works as expected.

Is this something that someone else has experienced?

Is it a bug or just a setting we're missing out on?