Bing Maps AJAX 7.0: get the current map style, even in automatic mode

var map = new Microsoft.Maps.Map(
    document.getElementById("map"),
    {
      credentials: "YOUR-BING-KEY",
      mapTypeId: Microsoft.Maps.MapTypeId.auto
    }
  );
 
  Microsoft.Maps.Events.addHandler(map, "imagerychanged", function(){
    var style = this.target.getImageryId();
    //
    // "style" contains the type of imagery being displayed
    //
  });