Okay *deep breath* - After a little consultation, I think there may be a few things going on here…
The first is that the ‘New Topic’ option in the menu is intended to show the current ‘mode’ of the topic, and had the wrong explainer description ‘Create a new topic linked to this topic’ included:
This should hopefully be tidied up with:
('New Topic' menu option has wrong description)
However, it is arguably a redundant option even with the right description if there’s no other state the topic can be in. 
(Why is there a 'New Topic' option in the composer menu when creating a topic?)
The original point about it appearing alongside the Post Voting toggle is also a valid one. 
For other things you can toggle on and off, like Shared Drafts or Staff Alias, it would show one or the other depending on what mode you were in (and would suppress that extra option if any of those features were enabled and available to the person creating the topic):
I think we need to make the Post Voting toggle behave in the same way as the others.
Lastly, the point @Moin raises about creating a New Topic from the main page and inheriting the options from the previous reply:
(New Topic composer menu inherits previous 'reply' options)
I think we need to split these into different topics so we can track them better. I’ll revert this one to be about the original post-voting toggle, and split off the others.