Warning: org.freedesktop.Platform.openh264 not installed

Context

I just tried running flatpak update with Flatpak 1.4.2.

Description

Here's what I saw:

$ flatpak update --system 
Looking for updates…


        ID                                           Arch              Branch           Remote            Download
 1. [✗] org.freedesktop.Platform.openh264            x86_64            19.08            flathub           593.6 kB / 593.4 kB

Warning: org.freedesktop.Platform.openh264 not installed
Installation complete.

There was a progress bar while org.freedesktop.Platform.openh264 was being downloaded, then it got replaced by the warning message.

Asking Flatpak to be more verbose doesn't help much though:

Proceed with these changes to the Default system installation? [Y/n]: y
Installing…                                                                                                                  F: Calling system helper: GetRevokefsFd
F: Calling system helper: GetRevokefsFd
F: flatpak_dir_pull: Using commit c0062d844eea58356fd6a153a29725c7fef7ee91df53ac759a535d1e5ee27a03 for pull of ref runtime/org.freedesktop.Platform.openh264/x86_64/19.08 from remote flathub
F: Loading https://github.com/cisco/openh264/releases/download/v2.0.0/libopenh264-2.0.0-linux64.5.so.bz2 using libsoup
Installing… ████████████████████ 100%  296.8 kB/sF: Received 592986 bytes
Installing… ████████████████████ 100%  296.8 kB/sF: Calling system helper: Deploy
Warning: org.freedesktop.Platform.openh264 not installed                                                                       
Installation complete.

Acceptance Criteria

The extension should install properly.

This is related with this flatpak issue: https://github.com/flatpak/flatpak/issues/3173