3.4: @content inside @at-root block throws an error

[TxHawks]

Title: 3.4: @content inside @at-root block throws an error

Including a @content statement inside an @at-root block (inside a mixin, of course) throws an error. This worked fine in 3.3.6.

Here is a reduced test case:

input.scss

@mixin test() {
  @at-root {
    @content;
  }
}

@include test {
  .test {
    property: value;
   }
 }

libsass 3.4.0:
Throws an error:

Error: Base-level rules cannot contain the parent-selector-referencing character '&'.

  Backtrace:
    input.scss:8, in mixin `@content`
    input.scss:3, in mixin `test`
    input.scss:7
 on line 8 of input.scss:7

ruby sass 3.4.21

.test {
  property: value;
}

version info:

$ node-sass --version
node-sass       4.1.1   (Wrapper)       [JavaScript]
libsass         3.4.0   (Sass Compiler) [C/C++]

[xzyfer]

Spec sass/sass-spec#1023