Issue:

• Mouse up event will be cancelled when multi-button down and release  the first one then the second one
• How to test: left press, without releasing left button right click, release left and right mouse button, you'll only see one release event
  Your browser does not support canvas.
• Source

  var stage, text;
   
  function init() {
          stage = new createjs.Stage("demoCanvas"); // Get EaselJS's stage to register to the canvas named "demoCanvas", can have multiple
   
  		linecount = 0;
   
  		text = new createjs.Text("Press:", "20px Arial", "#ff7700");
  		text.x = 10;
  		text.y = 10;
  
  		$('body').on('contextmenu', '#demoCanvas', function(event){ return false; });
   
  		stage.addChild(text);		
   
  		stage.addEventListener("stagemousedown", handleMouseDown);
  		stage.addEventListener("stagemouseup" , handleMouseUp);
  		createjs.Ticker.addEventListener("tick", tick);
      }
   
  function handleMouseDown(event){
  		text.text += "\r\n";
  		text.text += "Mouse Down Code = " + event.nativeEvent.button;
  	}
   
  function handleMouseUp(event){
  		text.text += "\r\n";
  		text.text += "Mouse Up   Code = " + event.nativeEvent.button;
  	}
   
  function tick(event){
  		stage.update();
  	}
   
  AJS.toInit( function(){
  	init();
  });