This is a known issue and I've discussed this with the support team some many times...but they don't get it. I gave up now.....
I guess if enough people complain, they might start listening.
It works fine on Homeaway and VRBO though. So what I do on Airbnb now is rather weird, but thats the only way I found to have it work. Here goes -> In the summer months of July and August, I only allow 1 week or multiples of a week. Due to this issue in Airbnb, I now block every even week off. This way, every odd week is shown as available and the only criteria I put is a minimum 7 day booking. This way people see that the entire week is available. The downside is that people can't book more than 1 week 😞 But this is better then getting no bookings. And then with each confirmed booking, I open the blocked weeks where it makes sense.
Hope this makes sense...........