CF7 does not transfer hidden date

I use CF7 to fill my database.
In the form I would like to enter today’s date (Date In)
and a specific date in the future (Date Out)
in the form.

Works wonderfully – actually. But only if the fields are visible to the user as normal.

If I set these fields to hidden, nothing appears in my database.

Works:
[date date-in “today”]
[date date-out “today+3 months”]

Does NOT work:
[hidden date date-in “today”]
[hidden date date-out “today+3 months”]

Why and is there a solution?