Bug in node-sass?

SassMeister-input.scss

@function rep-prop($prefix, $value...) {
  $rep:();
    @each $item in $value {
        @if(index($item, transform)) {
            $rep: append($rep, #{$prefix}$item, comma);
        } @else {
          $rep: append($rep, $item);
        }
    }
    @return $rep;
}
@mixin prefix($property, $value...) {
    @each $prefix in -webkit-, -moz-, -ms-, ''{
        #{$prefix}#{$property}: rep-prop($prefix, $value...);
    }
}
@mixin transition($properties...) {
    @include prefix(transition, $properties...);
}
@include transition(opacity 400ms ease-in-out, transform 400ms ease-in-out);

SassMeister-output.css

-webkit-transition: opacity 400ms ease-in-out, -webkit- transform 400ms ease-in-out;
-moz-transition: opacity 400ms ease-in-out, -moz- transform 400ms ease-in-out;
-ms-transition: opacity 400ms ease-in-out, -ms- transform 400ms ease-in-out;
transition: opacity 400ms ease-in-out,  transform 400ms ease-in-out;