And 1.3.0.beta5, at least for moving a post into a new topic (as moderator, not admin.).
The move post dialogue opens with PHP selected as the category. If you want to move the post to any other category, and select it from the dropdown, that’s fine; it works.
If you want to move it to PHP and leave it at the default - it will move with no category. If you actively select PHP from the dropdown - it will still move with no category. To move to PHP, you need to first select any other category and then switch it back to PHP.