Have you set the "Date Format" on the "Binding" tab, the "Display Pattern" on the "Field" tab and the "Validation Pattern" on the "Value" tab?
All of these fields need to match or be of a compatible pattern.
Here is how I achieved it:
Create a textfield, data format is plain text, type is 'Calculated, user can override'. In 'Calculated' event, place string to set rawValue, e.g. MM/DD/YY hh:mm. In 'Exit' event, parse the date, and the time separately, and check the format manually.