Start a screen, and have at least two windows in it. Get a different views
of the screen by running screen -x from another login (to the same account
of course). Make sure that this view is showing a different window in the
Type something in one view, then switch to the other view and press UP.
Nothing will happen, but if you go back to the first view you will see
that UP has been pressed there instead. Doing something other than
pressing UP or DOWN in the new view seems to fix this problem.
I have only confirmed that this happens (on two different machines,
though) when logging in via ssh.
Confirmed. What I'm guessing actually happens is that
just hitting up or down doesn't cause sceen to
switch to whatever screen is 'foreground' on the
current vt/pty/whatever you want to call it.
Fixed in screen-3.9.5, in Raw Hide.