Okular snap package cannot open URLs due to AppArmor

1) Ubuntu release: Ubuntu 17.10

2) Package version: Installed using “snap install okular”. “snap info okular” shows
snap-id: SfUqQ280Y4bJ0k64qtBKTTXq5ml46tvQ
tracking: stable
installed: 16.12.3 (3) 7MB -
refreshed: 2017-03-27 12:56:54 +0200 CEST

3) Expected behavior: Clicking a link in a PDF document opens the URL in an appropriate program (e.g. a browser).

4) Observed behavior: When clicking the link, Okular opens a window prompting to choose the application which should be used to open the URL. When choosing “Applications → Url handler script”, Okular displays the following error message:

KLauncher could not be reached via D-Bus. Error when calling start_service_by_desktop_path:
An AppArmor policy prevents this sender from sending this message to this recipient; type="method_call", sender=":1.411" (uid=1000 pid=29799 comm="okular /path/to/document.pdf ") interface="org.kde.KLauncher" member="start_service_by_desktop_path" error name="(unset)" requested_reply="0" destination="org.kde.klauncher5" (uid=1000 pid=32653 comm="/usr/lib/x86_64-linux-gnu/libexec/kf5/klauncher --")