Until a while ago, when I clicked on a collapsed thread, Thunderbird was selecting all messages of the thread (and then when, e.g., I pressed "delete" it deleted all the thread). After a recent upgrade (I believe it happened when LMDE installed Thunderbird 12.0.1), this behavior changed: now when I click on a collapsed thread it selects only the first message (and it displays it in the message pane, whereas before it was showing a summary of all messages of the thread). How can I revert to the previous behavior?
I don't believe it affects things, but I'm using IMAP.
In a related question (where the asker actually has the opposite problem) I read about the
mail.operate_on_msgs_in_collapsed_threads variable, but on my Thunderbird it's true.