Firebase.util - similar intersections with completely different results - angularjs

Question

I'm working on an angular project that uses Firebase as it's sole backend, angularFire for some synchronisation cases and I'm using this tool Firebase.util for dealing with shared resources. My case is this:
{
users {
user1 : {
tasks : {
active : {
task1 : true,
task2 : true
},
archived : {
task3 : true,
task4 : true
}
},
...
},
tasks : {
task1 : {
users : {
user1 : true,
user2 : true
}
},
...
}
},
}
and I'm dealing with the query like this:
var tasksRef = new $window.Firebase(FIREBASE_URL + '/tasks');
function _userActiveTasksRef(userId) {
return new $window.Firebase(FIREBASE_URL + '/users/' + userId + '/tasks/active');
}
function _userArchivedTasksRef(userId) {
return new $window.Firebase(FIREBASE_URL + '/users/' + userId + '/tasks/archived');
}
function getActive(userId) {
var interRef = $window.Firebase.util.intersection(_userActiveTasksRef(userId), tasksRef);
return $firebase(interRef).$asArray();
}
function getArchived(userId) {
var interRef = $window.Firebase.util.intersection(_userArchivedTasksRef(userId), tasksRef);
return $firebase(interRef).$asArray();
}
On the first case, when I intersect the active tasks with the "all tasks" ref everything works fine but when I try to perform the same operation with the archived tasks the intersection is always empty. I've already logged the individual queries and everything is working as expected, only the intersection doesn't seem to work. Is there any caveat that I'm missing? The two queries are being loaded at the same time if that matters.. the result is being stored in a controller like this:
this.tasks = {
active: tasks.getActive(currentUser.uid),
archived: tasks.getArchived(currentUser.uid)
};