Does anyone know why long prompt lines and window resizing causes lines of
terminal history to be removed?

I first noticed this while using tmux, but I can reproduce this issue
consistently both inside tmux and outside tmux (xfce4-terminal) with my
regular zsh dotfiles and with no zsh dotfiles at all on zsh 5.2. I also
tried with terminator terminal as well, but on resize it resets the
terminal history and the prompt appears at the top.

Steps to reproduce (without tmux):

   1. Make a super long prompt line (export PROMPT="this is a super long
   prompt line to test how zsh handles resizing of the window size when the
   prompt is crazy long like this one is going to be: ")
   2. Fill up the visible terminal window history with any text you want
   3. Make the terminal window as small as possible (both height and width)
   4. Make the terminal window as big as possible
   5. Rinse and repeat

Each time the terminal window goes big, the prompt moves up one line into
the terminal history and I lose that line. To reproduce in tmux it is
basically the same procedure. In a window with many panes laid out in a
tiled formation, zoom and un-zoom a single pane with a long prompt line a
couple of times.

-Aaron