Bootstrap gradient mixins with unlimited color-stops and prefixes.less

/* =============================================================================
   Gradients with unlimited color-stops
   ========================================================================== */

#gradient {

	// Filter color-stop params
	.color-stops(@color-stops-N...) {
		@color-stops: ~`"@{arguments}".replace(/(^\[)|(\]$)/g,'')`;
		@color-stops-webkit: ~`(function(c){
			for(var i=0; i<c.length; i++) {
				c[i] = c[i].trim().split(/\s+/);
				if(c[i].length==1)
					c[i].push(i==0?"0%":"100%");
				c[i] = "color-stop("+c[i].reverse().join(',')+")";
			}
	    	return c.join(",");
	    })("@{color-stops}".split(','))`;
	}

	// Creepy IE special treatment, fallback on first and last color-stop
	.ie-filter(@color-stops; @type) {
		filter: ~`(function(c,t){
	    	var a = c[0].split(/\s+/)[0].trim(),
	    		b = c.slice(-1)[0].trim().split(/\s+/)[0].trim();
	    	return "progid:DXImageTransform.Microsoft.gradient(startColorstr='"+a+"', endColorstr='"+b+"', GradientType="+t+")";
	    })("@{color-stops}".split(','),@{type})`;
	}

	// Horizontal gradient, from left to right
	.horizontal(@color-stops-0: #555 0%, @color-stops-1: #333 100%, @color-stops-N...) {
		.color-stops(@arguments);
		background-image: -webkit-gradient(linear, left top, right top, @color-stops-webkit); // Chrome, Safari 4+
		background-image: -webkit-linear-gradient(left, @color-stops); // Safari 5.1-6, Chrome 10+
		background-image: -o-linear-gradient(left, @color-stops); // Opera 12
		background-image: linear-gradient(to right, @color-stops); // Standard, IE10, Firefox 16+, Opera 12.10+, Safari 7+, Chrome 26+
		background-repeat: repeat-x;
		#gradient > .ie-filter(@color-stops; 1); // IE9 and down, gets no color-stop at all for proper fallback
	}

	// Vertical gradient, from top to bottom
	.vertical(@color-stops-0: #555 0%, @color-stops-1: #333 100%, @color-stops-N...) {
		.color-stops(@arguments);
		background-image: -webkit-gradient(linear, left top, left bottom, @color-stops-webkit); // Chrome, Safari 4+
		background-image: -webkit-linear-gradient(top, @color-stops); // Safari 5.1-6, Chrome 10+
		background-image: -o-linear-gradient(top, @color-stops); // Opera 12
		background-image: linear-gradient(to bottom, @color-stops); // Standard, IE10, Firefox 16+, Opera 12.10+, Safari 7+, Chrome 26+
		background-repeat: repeat-x;
		#gradient > .ie-filter(@color-stops; 0); // IE9 and down, gets no color-stop at all for proper fallback
	}

	.directional(@deg: 45deg, @color-stops-0: #555 0%, @color-stops-1: #333 100%, @color-stops-N...) {
		.color-stops(@arguments);
		background-image: -webkit-linear-gradient(@deg, @color-stops); // Safari 5.1-6, Chrome 10+
		background-image: -o-linear-gradient(@deg, @color-stops); // Opera 12
		background-image: linear-gradient(@deg, @color-stops); // Standard, IE10, Firefox 16+, Opera 12.10+, Safari 7+, Chrome 26+
		background-repeat: repeat-x;
	}

	.radial(@color-stops-0: #555 0%, @color-stops-1: #333 100%, @color-stops-N...) {
		.color-stops(@arguments);
		background-image: -webkit-gradient(radial, center center, 0%, center center, 100%, @color-stops-webkit); // Chrome, Safari 4+
		background-image: -webkit-radial-gradient(circle, @color-stops); // Safari 5.1-6, Chrome 10+
		background-image: -o-radial-gradient(circle, @color-stops); // Opera 12+
		background-image: radial-gradient(circle, @color-stops); // Standard, IE10, Firefox 16+, Opera 12.10+, Safari 7+, Chrome 26+
		background-repeat: no-repeat;
	}

	.striped(@angle: 45deg; @color: rgba(255,255,255,.15)) {
		#gradient > .directional(@angle, @color 25%, transparent 25%, transparent 50%, @color 50%, @color 75%, transparent 75%, transparent);
		background-repeat: repeat;
	}

}

There is a mistake an the directional method. Instead of @arguments you need to pass the colors only. If not the result will have 2 times the degrees.