AppArmor denial when trying to open file using content hub

Question

When trying to open a file using content hub using C++ I get these errors:

Opening with peer com.ubuntu.music_music_2.1.857
Sdk-Launcher> Application was resumed
Sdk-Launcher> There has been a AppArmor denial for your application.
Sdk-Launcher> Most likely it is missing a policy in the AppArmor file.
Syslog> Jun 20 19:15:23 ubuntu-phablet kernel: [ 3561.148570] type=1400 audit(1434827723.595:155): apparmor="DENIED" operation="open" profile="com.nogzatalz.downow_downow_0.8.81" name="/home/phablet/.local/share/applications/com.ubuntu.music_music_2.1.857.desktop" pid=9282 comm="downow" requested_mask="r" denied_mask="r" fsuid=32011 ouid=32011
transfer state changed to 5
Sdk-Launcher> Application was focused
transfer state changed to 5
transfer state changed to 5

I checked in the Transfer::State enum and found that state 5 means aborted.
This is my apparmor.json file:

{
    "policy_groups": [
        "networking",
        "content_exchange",
        "content_exchange_source",
        "audio"
    ],
    "policy_version": 1.3
}

I'm using the ubuntu-sdk-15.04-qml framework.
My app worked fine until the last OTA update. On my Nexus 5 this is r20.
Any help is appreciated!

EDIT: After trying to solve this problem for a while, I noticed that I'm able to import content from other applications, but exporting still doesn't seem to work.
Here is my simplified code for importing (which works):

QPointer<cuc::Hub> hub = cuc::Hub::Client::instance();
cuc::Peer peer = hub->default_source_for_type(cuc::Type::Known::pictures());
cuc::Transfer * t = hub->create_import_from_peer(peers);
t->start();

Here is my simplified code for exporting (which doesn't work):

 QPointer<cuc::Hub> hub = cuc::Hub::Client::instance();
 QVector<cuc::Peer> peers = hub->known_destinations_for_type(cuc::Type::Known::pictures());
 cuc::Transfer * t = hub->create_export_to_peer(peers[0]);
 QVector<cuc::Item> items;
 items.append(cuc::Item(QUrl::fromLocalFile("/home/phablet/.local/share/com.nogzatalz.downow/download/Ed Sheeran – 5 (2015) (ALBUM) 320 KBPS/Cover.jpg")));
 t->setSelectionType(cuc::Transfer::single);
 t->charge(items);

Answer 1

In my manifest.json, I had to add a property called content-hub to hooks:

"content-hub": "hub.json"

And then create a hub.json file:

{
    "source": [ "pictures" ]
}