I just checked and, sure enough, you are correct.
In a haste last night, I replied to an inquiry from the HA app for Christmas and, sure enough, the dates are blocked on my linked calendars simply because I answered a question for a potential guest.
It's been said here many times not to use the app for this very reason but I didn't know it also blocked the dates on my linked calendars... I won't be lazy again.
I think the best work-around is to NEVER respond from the app and always reply from the website which allows you to reply without pre-approval. If you do that it shouldn't block any dates on any calendar. Now I am not sure and will have to check but I think that's the way to do avoid this issue until Vrbo/HA fixes this issue -- and it IS an issue. A BIG issue.