title: How to fix GNUPLOT replot issue
body: <p>I set-up a multiplot like this:</p>
  
  <pre><code>set terminal wxt size 1500,900
  set format x "%d%m%y %H:%M:%S"
  set xdata time
  set timefmt x "%Y%m%dT%H%M%S"
  set key font ",6"
  set lmargin 10
  set rmargin 10
  set multiplot layout 2,1
  plot "output.txt" u 1:2 w lines axes x1y1, \
  "output.txt" u 1:3 w lines axes x1y2
  plot "output.txt" u 1:40 w lines axes x1y1, \
  "output.txt" u 1:39 w lines axes x1y2
  set y2tics border
  unset multiplot
  </code></pre>
  
  <p>Which works, and gives me 2 plots, one above the other.</p>
  
  <p>But pressing the "replot" button (or using zoom) causes the second plot to fill the window - completely hiding the first plot.</p>