Date fields (or any field type) should not be resizable smaller than the minimum required to display the data. It does not make sense that I can add a date field, but size it small enough that I can't actually read the date. If the field requires entering the day, month, and year to the field, I should not be able to de-size the field to the point that I can't see part of that date.

Otherwise, if there are use-cases where de-sizing it and obstructing the field is useful, there should be a lock/unlock option on fields so you can toggle maintaining the minimum size.