I'm trying to paste a template in the 2017 wikitext editor (following the instructions provided by the {{non-free reduce}} template).
When I copy and paste the template code, {{subst:orfurrev}}, it is transformed into the following nonsensical code:
<nowiki>{{</nowiki>[[Wikipedia:Substitution|subst]]:[[Template:Orfurrev|orfurrev]]<nowiki>}}</nowiki>
Edit: I've noted that this only happens when I copy the text from the HTML page, not when I copy it from a plain text editor, so this is likely related to the text formatting.
The primary advantage of wikicode is that it is plain text. The wikitext editor should make exactly zero magic transformations, treating everything copied or pasted as a raw Unicode string without formatting. Any such magic should be handled as optional suggestions and provided as an opt-in; otherwise the use case for an enhanced wikitext editor, which gets confused by trivial text paste operations, is doomed to fail.
Oh, and while in Beta (and possibly after that), there should be an easy way to access the classic Wikitext editor. Now in order to edit the page I was working on, I'll have to disable the 2017 editor in the Preferences/Beta options, and I'm not sure I'll re-enable it again. In fact I expected the "edit source" link to me to the classic editor, and that the 2017 editor would be accessible only through the [[ ]] button in the Visual Editor.