Unexpected extracted variable in second looped ruleset

A variable extracted from a list has a different value than expected, but not during the first mixin loop.

An example is:

@list: red, blue, green;

.loop(@rules, @index: length(@list)) when (@index > 0) {
  @el: extract(@list, @index);
  
  @rules();
  
  .loop(@rules, @index - 1);
}

.loop({
  .a { 
    color: @el;
  }
});

.loop({
  .b { 
    background-color: @el;
  }
});

I expect three .a and three .b with the three different colors but I get (https://lesscss.org/less-preview/ 2021-09-09):

.a {
  color: green;
}
.a {
  color: blue;
}
.a {
  color: red;
}
.b {
  background-color: green;
}
.b {
  background-color: green;
}
.b {
  background-color: green;
}

Checking the value before the @rules(); call, I get the expected color:

  .test {
    current: @el;
  }
  @rules();

.test {
  current: green;
}
.a {
  color: green;
}
.test {
  current: blue;
}
.a {
  color: blue;
}
.test {
  current: red;
}
.a {
  color: red;
}
.test {
  current: green;
}
.b {
  background-color: green;
}
.test {
  current: blue;
}
.b {
  background-color: green;
}
.test {
  current: red;
}
.b {
  background-color: green;
}

Adding index: @index; near current, color and background-color has always the expected values.
Only the extracted @el is fixed in the second loop.

Since @list and @index are correct during the ruleset evaluation, if I extract the value inside the ruleset it works as expected:

.loop({
  @el: extract(@list, @index);
  .b {
    background-color: @el;
  }
});

.b {
  background-color: green;
}
.b {
  background-color: blue;
}
.b {
  background-color: red;
}

Start with the recursive Less mixin reproduction in the issue and compare the first loop's extracted @el with the second loop's behavior around @rules(). Check the alternate example that extracts @el inside the ruleset. Done means the original example emits green, blue, and red for both .a and .b rules.