Version: 1.11.4 (using KDE 4.2.4) OS: Linux Installed from: Slackware Packages I remember that in previous version of KMail (I think around KDE4.0) selecting all messages in the message list with CTRL+A would only select the "visible" messages, which were visible because the groups in which they were, were expanded. Now, when selecting all messages, it expands and spans across collapsed groups, and select, well, all messages in the current folder. I think the select all message feature should honor the collapsed groups, and don't mind the hidden messages.
testing with KDE 4.3.1, CTRL-A (select all messages) only the visible messages. In collapsed threads, only the first mail is selected.