The input in the DateTimePicker is valid when:

- the DateTimePicker value is bound to nullable DateTime and

- the user clears the input

In such cases, the input field shouldn't get a red border.

Here is a REPL example to reproduce the issue:

1. Select a date.
2. Clear the date. The input gets a red border.

===ADMIN EDIT===

A possible workaround is to change the border color with CSS. Here is a REPL example.