Strange less-syntax bug about less-plugin-clean-css HOT 10 CLOSED

@isresponsive: true;
@font-size-base: 16px;

// Universal value setter
.set-value_(@property; @value; @responsive: @isresponsive) {
  // String, percentage and relative unit values
  .setter(@p; @v) when not (isnumber(@v)), (ispercentage(@v)), (isem(@v)), (isunit(@v, rem)),
                           (isunit(@v, ex)), (isunit(@v, ch)), (isunit(@v, vw)), (isunit(@v, vh)),
                           (isunit(@v, vmin)), (isunit(@v, vmax)) {
    @{p}+_: @v;
  }
  // Non-unit and pixel values
  .setter(@p; @v) when (default()) {
    & when (@responsive) {
      @{p}+_: unit((@v / @font-size-base), rem);
    }
    & when not (@responsive) {
      @{p}+_: unit(@v, px);
    }
  }
  .setter(@property; @value);

  // Font support
  & when (@property = font) {
    @check: ~`function(){var v="@{value}";return !!v.match(/\//)}()`;
    @v1-value: ~`function(){var v="@{value}";return parseFloat(v=v.replace(/^(\d+).*\/(\d+).*$/, '$1'))}()`;
    @v1-unit: ~`function(){var v="@{value}";return v=v.replace(/^\d+(.*)\/\d+(.*)$/, '$1')}()`;
    @v2-value: ~`function(){var v="@{value}";return parseFloat(v=v.replace(/^(\d+).*\/(\d+).*$/, '$2'))}()`;
    @v2-unit: ~`function(){var v="@{value}";return v=v.replace(/^\d+(.*)\/\d+(.*)$/, '$2')}()`;
    & when (@check) {
      .set-value(font-size; unit(@v1-value, @v1-unit); line-height; unit(@v2-value, @v2-unit); @responsive);
    }
  }
}
.set-value(@args...) when (length(@args) > 1) {
  .r(@a) when (extract(@a, length(@a)) = true), (extract(@a, length(@a)) = false) {
    @l: (length(@a) - 1);
    @responsive: extract(@a, length(@a));
  }
  .r(@a) when (default()) {
    @l: length(@a);
    @responsive: @isresponsive;
  }
  .r(@args);
  .i; .i(@i: @l) when (@i > 1) {
    .i((@i - 2));
    @property: extract(@args, (@i - 1));
    @values:   extract(@args,  @i);
    .j(@property; @values; @responsive);
  }
  .j(@p; @v; @r; @j: length(@v)) when (@j > 0) {
    .j(@p; @v; @r; (@j - 1));
    .set-value_(@p; extract(@v, @j); @r);
  }
}

.set-value(font; 14px/230% 'Arial'; margin: 0 16 0 0);