Sprint Calendar differs from DatePicker Format

[ChristopherChilds]

Hi All,

we some strange behaviour,

When we edit a sprint in our Live Jira instance, we are seeing that the Calendar does not follow the defined ISO format for the DatePicker Field. Link Here

This is what we see when we create a sprint. As you can see it says (incorrectly) Sunday if the first day of the week:

Whereas when using the DatePicker Field for an issue it (correctly) says Monday is the first day of the Sprint:

I have checked the ISO settings under Look and feel are the same and I searched for Date setting in Advanced Settings
I have also tested with more than one browser.