I would have expected the following : 

  var bounds = new google.maps.LatLngBounds(new google.maps.LatLng(-
35, 170), new google.maps.LatLng(-45, -170));
  console.log(bounds.toSpan().lng()) // 20
  gmap.fitBounds(bounds);

to zoom the map in to roughly fit New Zealand.  Instead I get an extremely 
zoomed-out map, showing the entire world.

The bounds variable in my example appears to be successfully set up to be 
a rectangle crossing the 180 longitudinal meridian (note the span has a 
longitude of 20 degrees), but fitBounds ignores this and seems to try to fit 
the very wide rectangle starting at -170, and taking the long way round to 
get to +170.

Is this a known problem?