strange gradient occurenece

I have a for statement that creates a series of gradient boxes. On the last box a clear diagonal line shows. Does anybody have a clue why this may be?

        // Draw gradient
        with (this.headLineBackboard) {
            colors = [0xFFFFFF, 0xFFFFFF];
            alphas = [100, 00];
            ratios = [0, 0xFF];
            matrix = {matrixType:"box", x:1.5, y:1.5, w:180, h:50, r:(0/180)*Math.PI};
            this.beginGradientFill("linear", colors, alphas, ratios, matrix);
            this.lineStyle(0, 0x000000, 0);
            this.lineTo(0,50);
            this.lineTo(180, 50);
            this.lineTo(180, 0);
            this.lineTo(0, 0);
           
            this.endFill();
        }