tmux: unknown option -- X

I want to add "me too" but I'm using a different version of tmux. My statusbar is not showing <F5> permanently since the 5.16 update.

byobu:
  Installed: 5.16-0ubuntu1~ppa5
  Candidate: 5.16-0ubuntu1~ppa5
  Version table:
 *** 5.16-0ubuntu1~ppa5 0
        500 http://ppa.launchpad.net/byobu/ppa/ubuntu/ oneiric/main i386 Packages
        100 /var/lib/dpkg/status
     4.37-0ubuntu1 0
        500 http://nl.archive.ubuntu.com/ubuntu/ oneiric/main i386 Packages
tmux:
  Installed: 1.5-1
  Candidate: 1.5-1
  Version table:
 *** 1.5-1 0
        500 http://nl.archive.ubuntu.com/ubuntu/ oneiric/universe i386 Packages
        100 /var/lib/dpkg/status

I have the same problem with

$ byobu --version
byobu version 5.18
tmux 1.6

from the Gentoo ebuilds running in Konsole 2.8.4 (KDE 4.8.4). There are actually many more Byobu commands that try to call tmux -X, e.g.

$ byobu-quiet --undo
tmux: unknown option -- X
usage: tmux [-28lquvV] [-c shell-command] [-f file] [-L socket-name]
            [-S socket-path] [command [flags]]

Any code like $BYOBU_BACKEND -X won't work in tmux, at least not in version 1.6.

Here are the other occurrences of such code:
$ fgrep -- "BYOBU_BACKEND -X" `qlist byobu`
/usr/lib64/byobu/date: [ "$bd" = "0320" ] && msg="$(printf "%s" SGFwcHkgQmlydGhkYXkgU2NyZWVuIC0tIGh0dHA6Ly9iaXQubHkvc2NyZWVuLWJkYXkK | base64 -di)" && $BYOBU_BACKEND -X -S "byobu" at "*" echo "[$msg]"
/usr/bin/byobu-ctrl-a: $BYOBU_BACKEND -X at 0 source "$BYOBU_CONFIG_DIR/profile"
/usr/bin/byobu-ctrl-a: $BYOBU_BACKEND -X at 0 source "$BYOBU_CONFIG_DIR/profile"
/usr/bin/byobu-disable: $BYOBU_BACKEND -X at 0 quit
/usr/bin/byobu-quiet:$BYOBU_BACKEND -X at 0 source "$BYOBU_CONFIG_DIR/profile"
/usr/bin/byobu-select-profile: $BYOBU_BACKEND -X at 0 source "$BYOBU_CONFIG_DIR/profile"

Confirmed. Looking...

Committed revision 2021.