Detached ruleset unlocked from namespaced mixin does not see its namespace scope

I defined a detached ruleset inside a namespaced mixin. The ruleset is unable to see variables defined in its outer namespace.

Less:

#namespace {
  @variable: in-namespace;
  .unlocker {
    @detached-ruleset: { property: @variable; };
  }
}
#namespace > .unlocker();

#detached-ruleset {
  @detached-ruleset();
}

actual output:

NameError: variable @variable is undefined in test.less on line 4, column 36:
3   .unlocker {
4     @detached-ruleset: { property: @variable; };
5   }

expected output:

#detached-ruleset {
  property: in-namespace;
}

Edit: I use node.js with lessc 1.7.0 (LESS Compiler) [JavaScript]
Edit 2: this issue is probably related to #2039

Start by running the minimal Less example with lessc, using the namespaced mixin and detached ruleset shown in the report. Trace how the detached ruleset is unlocked and resolve its namespace scope; done means the output contains property: in-namespace instead of the undefined-variable error.