max_date_allowed is min excluded date in reality. Date provided to that argument is not selectable. Is that intended behavior or simple off-by-one error?
Also, with clearable=False backspace can still clear date, but on action it will pop back in. I think that date field should be editable only from calendar view with clearable=False, or add something like editable? (when with_portal=True it is not reproducible as backspace does not fall ‘behind’ portal)