1.12.1 - :not selector issue

[chriscdg]

We recently upgraded from 1.11.4 to 1.12.1 and noticed a bug that seems to be around the :not selector.

When using 1.11.4:
SCSS

.form-group {
  label:not(.col-form-label,.form-check-label,.radio-inline,.form-label-static) {
    position: absolute;
    top: 0.6rem;
    left: 1.1rem;
  }
}

Output CSS

.form-group label:not(.col-form-label):not(.form-check-label):not(.radio-inline):not(.form-label-static) {
  position: absolute;
  top: 0.6rem;
  left: 1.1rem;
}

When using 1.12.1
SCSS (Same as above)
Output CSS

.form-group label {
  position: absolute;
  top: 0.6rem;
  left: 1.1rem;
}

Please let me know if you need any more information, or if maybe this is a symptom of a different problem. Thanks!

EDIT: It looks like this only affects nested :not selectors. When I change the SCSS to

.form-group label:not(.col-form-label,.form-check-label,.radio-inline,.form-label-static) {
    position: absolute;
    top: 0.6rem;
    left: 1.1rem;
}

Then it works properly.

[glebm]

This was a bug in libsass: sass/libsass#2697
Fixed on libsass master: sass/libsass#2736