A few packages are effectively rolling even in the stable distribution, because they have a high volume of security fixes and it's a high-impact application. We just don't have the resources to backport all the fixes. This isn't completely unlike debian's treatment of e.g. firefox which keeps even its `oldstable` distribution up to date with "latest" ESR (correct me if I'm wrong).

There are still debates in the community over what the stable distribution is "for", so you may occasionally see some inconsistencies in what gets bumped and what doesn't.