Greeter frozen at login with bluetooth keyboard (eOS8 latest)

[codecowboy]

I've got a weird issue with both a usb keyboard and bluetooth keyboard 'attached' in eOS8 (all updates applied). At boot, the password field in the greeter won't accept keystrokes / is disabled in some way with both keyboards active. If I switch to tty, I can use both keyboards. If I switch the bt keyboard off and reboot, I can use the usb keyboard as usual to login at the greeter screen. Can someone give me a steer on what might be causing this? I couldn't find anything obvious in journalctl or dmesg. I'm guessing it's not the usb or bluetooth stacks if the tty works. Would it be lightdm? I'm not 100% sure of the display stack but think it goes something like xorg/lightdm/mutter (gala?)/ pantheon? Would be grateful for any troubleshooting tips or advice on where to look for errors. Ironically, the reason for wanting to have both keyboards is to avoid any bluetooth connection issues while I am configuring things. Thanks!

[codecowboy]

There is much more detail, including logs etc here: elementary/greeter#770 . I put it there as an issue had already been raised. N.B I don't think USB is involved, that's just what I had connected at the time.