matplotlib/seaborn: first and last row cut in half of heatmap plot

Unfortunately matplotlib 3.1.1 broke seaborn heatmaps; and in general inverted axes with fixed ticks.
This is fixed in the current development version; you may hence

• revert to matplotlib 3.1.0
• use matplotlib 3.1.2 or higher
• set the heatmap limits manually (ax.set_ylim(bottom, top) # set the ylim to bottom, top)