Version 3.x.x breaks pseudo selector extensions

[fatlard1993]

The following example works in 2.x.x and not in 3.x.x:

.test {
  display: none;
}

.thing:before {
  @extend .test;
}

[romainmenke]

This has since been fixed.

On the latest version I get :

.test {
    display: none;
}

.thing:before {
    display: none;
}