@pcottle @mosseri This is not a Mastodon client. It’s how Pleroma, Akkoma, and other forks display images from Threads.
And yes, I’ve tested this on multiple front-ends and clients—same result. Other people running Akkoma and Pleroma report the same thing.
Both Akkoma and Pleroma, by the way, utilize Mastodon’s API.
One further thing: behind Mastodon and Misskey, Pleroma/Akkoma is the third most used microblogging server software on the Fediverse, particularly popular with people who run small servers and care about resource efficiency. It’s used by around 200,000 people. As more people run their own servers, it will likely be even more popular in the future.