Steps:

1. Go to Content/Content structure.
2. Click Create and select Form.
3. Start creating Form, add Date field.
4. Try to exit Form builder.

Actual result:
Validation occurs Field has invalid configuration. But when user open settings and just click Submit, validation disappears. It looks like date format is not set as default.

Expected result:
Default date is set so there is no problem with the validation. Proposed date format

 mm/dd/yyyy 

Remarks:
When adding Date field console shows:

 POST http://ee-2.4.0.ub/admin/form/preview 500 (Internal Server Error)