title: Matplotlib newline character in xtick label
body: <p>I've seen a bunch of solutions (including matplotlib example code) that to have an x-tick label be multi-line you can just introduce a newline character. Which I did (below is a code excerpt that adds this newline):</p>
  
  <p><code>
  subplot.xaxis.set_major_formatter(mdates.DateFormatter("%m-%d\n%H:%M", tz=startTime.tzinfo))
  </code></p>
  
  <p>However, I noticed this introduces a weird quirk in which when I mouse-over the plots it kind of causes all the plots to 'jump' up and down (shift slightly up and then back down when I mouse over again). Note: if there is just one plot then the bottom matplotlib toolbar (with the save button etc..) shifts up and down only. This makes it unpleasant to look at when you are trying to move the mouse around and interact with the plots. I noticed when I take out the new-line character this quirk disappears. Anyone else run into this and solve it (as in keeping multiline label without this weird 'jump' quirk)?</p>
  
  <p>I'm using Python 3.6 and matplotlib 1.5.3. using TKAgg backend.</p>