Hogwild ProseMirror is a dokuwiki plugin
Apologies, I didn't know this particular plugin.
Hogwild You misquoted me.
I did not. I quoted part of your very first post in this thread. You can see where a quotes is taken from by clicking on the link with your user name in front of the quote.
Well, anyway. Having learned that ProseMirror was a DokuWiki plugin, I took a quick lock at its documentation.
I tried editing the document provided in the sandbox: https://wysiwyg.wiki.cosmocode.de/doku.php?id=en:playground:start
I copied formatted text from that page and pasted it somewhere else on the same page. The pasted text looks exactly the same, with all formatting. I did this in both modes ('Syntax' editing and 'Wysiwig' editing), and copying & pasting worked in both instances.
I wouldn't trust this method, however, when copying parts of elements, as the semantics of this kind of operation might not always be clear and the results therefore not quite what I'd expect them to be.
The documentation also says that ProseMirror is still in Beta. This means that it's possible that not all functions work as advertised for everyone. The documentation also says that it's unknown whether it works in the more recent versions of DokuWiki.
Anyway, you didn't tell us which version of DokuWiki you are using, and we don't know the particulars of the documents you are trying to edit, so I can't know why it doesn't work for you.
I am changing the tags for this thread (again) and move it to the plugins section.