A gap in 360 degree canvas arc

A gap in 360 degree canvas arc

Why there is a gap in 360 degree arc
ctx.beginPath();
ctx.moveTo(100, 100);
ctx.arc(100, 100, 100, 90 * Math.PI / 180, 450 * Math.PI / 180);
and arc from 0 to 360 have not
ctx.beginPath();
ctx.moveTo(310, 100);
ctx.arc(310, 100, 100, 0 * Math.PI / 180, 360 * Math.PI / 180);
http://jsfiddle.net/YMtdZ/4/
It's a bug or I'm doing something wrong?