I almost created a new topic with an html5 problem, but I managed to find a fix.
Basically, in HTML5, you get an extra line between the end of a curveTo and the first moveTo.
Setting a new moveTo after the curveTo to avoid this error.
graphics.lineStyle(25, 0x990000, 1);
graphics.moveTo(200, 200);
graphics.curveTo(400, 300, 200, 500);
graphics.moveTo(400, 200); //This line is not need in flash