@at-root with dynamic selector doesn't work

[chriseppstein]

.test .testa {
  @at-root #{"%foo"} {
    color: red;
  }
  @extend %foo;
}

Compiles to:

.test .testa .testa {
  color: red;
}

Instead of the expected:

.test .testa {
  color: red;
}

If @at-root #{"%foo"} is changed to @at-root %foo it works as expected but these two should be semantically identical.

cc: @eoneill

[mgreter]

Duplicate of #1210 and will be fixed once my latest refactoring is merged: #1249!

[xzyfer]

Specs added sass/sass-spec#419

[mgreter]

We now have a passing spec test since #1249 was merged 🎈