Date format is not taken into account for custom field on activity import

I defined custom fields for Activities, one of them is of Date type. When I try to import activities, I've got an error for some of them telling that the date for this custom field is invalid. I've chosen dd/mm/yyyy as date format and I've realized that it only happens when the day is greater than 12 - the maximum month number.

I think that the date format is not taken into account for custom fields when importing activities.