DateTime field with i18n - the value displayed in the UI is wrong when `i18n` is set to `duplicate`

[dallyh]

Hello,

as the title says (this again might be just an UI thing), when there is a field set up for a collection like this:

{
          "name": "pubDateTime",
          "label": "Publish Date",
          "widget": "datetime",
          "i18n": "duplicate",
          "date_format": true,
          "time_format": true
},

Then, when creating a new entry in the UI the field's value is in the other locale (not default locale) is not set (or it looks like it - screenshot taken from split view i18n side by side):

Also when I turn off i18n side by side, this happens (mask is displayed):

Then when I switch back, both fields are displaying the mask:

The actualy value is saved into the entry (file) even though in the UI it looks different:

Started happening on version 4.0.0.