TAdvDBDateTimePicker NullDateFormat causing problems to show/edit values

With AdvDBDateTimePicker, there are problems when NullDateFormat and Format are different.
I try to show it blank, or something like (n/a) when the field value is null. It works, but when I have to input some value, it seems to mantain the nulldateformat, so I cannot type, and it neither shows the selected date when I use the drop down calendar (I must scroll the dataset or reopen the form to see the selected value reflected).

For example, I put Format as 'dd/MM/yyyy', and try to use NullDateFormat as '' (literally 2 single quotes), or as ''(n/a)'', with DateMode dmComboBox, DateFormat = dfShort, Kind=dkDate, ShowCheckbox = True, but it randomly let/don't let edit the field when alternating from null to valid values.

What should be the best approach on how to use the NullDateFormat to avoid showing the user something like a grayed 31/12/1899 ?

I see no issue here when setting NullDateFormat to a space.
When there is a null date in the DB, it shows as blank in the TAdvDBDateTimePicker, otherwise it displays a fully formatted date.