Anthony Anson noted:
Thunderbird wanted to reply straight to you and not the list - have any of my other replies to list gone back to author, anybody?
Must watch this, and adjust something if so.
Mozilla Thunderbird has a known bug: it doesn't support email lists! https://bugzilla.mozilla.org/show_bug.cgi?id=29041
Nine years on and still no fix in sight, but there is an extension at http://www.juergen-ernst.de/addons/replytolist.html which might fix it for you.
Hope that helps,