Missing constants possibly related to mixed c/rb and nested classes

Minimal test case to reproduce:

Create two files,

async.rb:

class Xmms::Collection::Async
end

collection.c:

void
Init_Collection()
{
    mXmms = rb_define_module("Xmms");

    cColl = rb_define_class_under(mXmms, "Collection", rb_cObject);

    /* Document-const: Xmms::Collection::NS_ALL
     *
     * I am documentation */
    rb_define_const(cColl, "NS_ALL", rb_str_new2(XMMS_COLLECTION_NS_ALL));
}

Build with:
rdoc async.rb collection.c

And notice the lack of the NS_ALL constant.

Reproduce the issue with the shown async.rb and collection.c files using rdoc async.rb collection.c, then inspect how RDoc combines Ruby nested classes with C extension declarations. Done means the generated documentation includes the documented Xmms::Collection::NS_ALL constant.