A canvas transparent fillStyle test case

function draw() {
	var canvas = document.getElementById('canvas');
	var ctx = canvas.getContext('2d');

	// assign gradients to fill and stroke styles
	ctx.fillStyle = 'rgba(0,0,0,0)'; // or 'transparent'
	ctx.fillRect(50,25,50,100);
	
	// setting fillStyle to anything other than 'transparent' will fix this case.
	// ctx.fillStyle = 'red';
	
	ctx.strokeStyle = 'green';
	ctx.lineWidth = 5;
	ctx.beginPath();
	ctx.moveTo(canvas.width/4, canvas.height/2);
	ctx.lineTo(canvas.width *3/8, canvas.height * 3/4);
	ctx.lineTo(canvas.width * 3/4, canvas.height /4);
	ctx.stroke();
}