It is already the case. See `org-adaptive-fill-function': it returns nil
when at a node property.
I thought so too, because the filling doesn't happen on M-q. So it took me a while to come with that complete ECM.
I cannot reproduce your ECM.
Did you copy and paste the whole ECM including the Local Variables? .. because I can reproduce that in emacs -Q (emacs-26 branch).
It's something about auto-fill-mode being on, that's different from M-q.
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