I am on Slackware 14.2, which comes with tmux-2.1.
My $TERM bash variable is set to 'screen' when entering tmux, whereupon pressing Ctrl+l (the usual shortcut to clear the screen) simply produces a new line rather than actually clearing: the behavior is identical to pressing 'Enter'. The same happens with any other shortcut I bind to clear-screen in my .inputrc file. So it seems clear-screen is interpreted as a new line.
Simply issuing the command 'clear' works however, as does 'Ctrl+l' when I start screen rather than tmux (even though in screen the $TERM variable is still 'screen').
I have also briefly packaged and installed the latest tmux I could
clone from git with exactly the same results, so this is not due to the relatively old version of tmux.
Finally, it is not clear to me whether this is in any way related to
this other tmux problem I posted earlier.