Client doesn't receive keyboard input if it started before the keyboard was connected

When I don't have any input device connected, I run a client and then connect a keyboard, the client doesn't start receiving input from the keyboard.

Reproducing this is pretty easy:

1. Run Weston with these settings:

[core]
backend=drm-backend.so
shell=kiosk-shell.so
require-input=false

2. Run weston-fullscreen client, for example
3. Connect a keyboard
4. The client won't receive any input from the keyboard

If you reverse the order and you first connect the keyboard and then run the client, it receives the keyboard input properly.