The intention was that C-b would move the designated window into the
current window but the command was incorrectly written such that the
active pane would be moved into the designated window instead.
# Move the current pane into a separate window.
bind b break-pane
# Split another pane into this window.
-bind B command-prompt -p "Select [<window>.]<pane> to join:" 'join-pane -t %1'
+bind B command-prompt -p "Select [<window>.]<pane> to join:" 'join-pane -s %1'
# Next pane.
bind i select-pane -t :.+
bind C-i select-pane -t :.+