The important thing about a pinned ad is that it is seen by everyone.
It’s fine to auto-unpin when a user has clicked and fully read the advert. There’s no reason to keep presenting the same advert to a user once they’ve clicked and read it once.
The important thing for an advertiser is that they see some evidence that their topic has been pinned.
Because of the way auto-unpin currently works (without my fix), the author of a pinned topic never once sees it as pinned — and naturally this is disconcerting for advertisers who have paid for the privilege.