Exactly right. They are attempting to incorporate it into their actual branding iconography so that they can argue it's trademark.

Yup! Copyright and trademark are different things and Disney lawyers have already insulated the company. Yes it will technically enter public domain, but nothing will actually change.

Jokes on Disney, I'm making my porno about Captain Pete, who drives his steamboat down the river, picking up floozies and spitting tobacco up their butts.

(We are all making porn right? That's the plan.)

I actually think this is a good way to do things, the original work becomes public domain and can be freely reproduced, but people can't, for example, make NSFW versions of the work.

Or just a conga line of shitty Sherlock Holmes adaptations.