Parallel extends do not inherit styles

TL;DR: .B is nested inside .A. If .A1 extends .A and .B1 extends .B, I would expect that .A1 .B1 {} would inherit the same styles as .A .B {}. However it does not.

Demo here.

/*-----------*\
  less input:
\*-----------*/
.title {
    .firstpara {
        margin-top: 0;
    }
}
.title-main {
    &:extend(.title all);
}
.firstpara-main {
    &:extend(.firstpara all);
}


/*----------------*\
  returned result:
\*----------------*/
.title .firstpara,
.title-main .firstpara,
.title .firstpara-main {
    margin-top: 0;
}


/*----------------*\
  expected result:
\*----------------*/
.title .firstpara,
.title-main .firstpara,
.title .firstpara-main,
.title-main .firstpara-main {
    margin-top: 0;
}

Start with the linked CodePen reproduction and compare the generated selectors with the expected output in the issue. Trace the handling of parallel nested extends, then verify that the combined .title-main .firstpara-main selector is generated without regressing the existing selectors.