Regression: 'Sound keys' a11y feature doesn't work on Wayland session start until re-enabled

Affected version

• Arch Linux, updates till 2021-04-24T08:33:31+0300
• mutter 40.0+55+gf4f82bcb-1 gnome-settings-daemon 40.0.1-1
• Wayland only, X11 session continues to work as earlier

Bug summary

After upgrade from 3.38 to 40 Mutter doesn't signal Caps&Num Lock switch until I open A11y settings and re-enable the 'Sound Keys' feature.

Steps to reproduce

1. Enable 'A11y' → 'Sound Keys'.
2. Log out (or reboot).
3. Log into Wayland session.
4. Press Caps Lock.

What happened

No sound.

What did you expect to happen

Session plays system notification sound.

Relevant logs, screenshots, screencasts etc.

My X11 system still produces the sound from boot. It's Arch Linux too, with the same Mutter and GSD.

Through dconf editor I can see the setting enabled while there is still no sound.

Audio works generally, like Pidgin notifications or Volume change sound.

Toggling a sibling feature doesn't make this one work. Only re-enabling helps.

Once works, doesn't break when switching users (i.e. without logging out).

From what I found the feature was implemented for Wayland in !614 (merged) (#637 (closed)).