Field emptied when filled with a non-existing i18n code

When filling a field in element properties, I can select an i18n key for the value by using i18n: in front of the label text (see screenshot). However, when I fill in a non-existing i18n code here (because I tend to add the label to an element first, and afterwards create the i18n key for it), the field will be emptied when I press Enter.

I have to click outside of the dropdown to leave the i18n key in. I'd prefer the label to stay there even if it's not an existing i18n key. Or maybe better even: notify the user that the i18n key doesn't exist yet, and allow them to enter a default value in a prompt or something.