PS/2 mouse and keyboard not disabled when adding USB devices

Host environment

• Operating system: ArchLinux
• OS/kernel version: Linux x280 6.6.1-arch1-1 #1 SMP PREEMPT_DYNAMIC Wed, 08 Nov 2023 16:05:38 +0000 x86_64 GNU/Linux
• Architecture: amd64
• QEMU flavor: qemu-system-x86_64
• QEMU version: 8.1.2
• QEMU command line:

  qemu-system-x86_64 -cpu host -M q35 -device qemu-xhci,id=xhci -usbdevice tablet -usbdevice keyboard -enable-kvm -smp 12 -m 8G -hda haiku.qcow2

  or

  qemu-system-x86_64 -cpu host -M q35 -device qemu-xhci,id=xhci -device usb-tablet -device usb-kbd -enable-kvm -smp 12 -m 8G -hda haiku.qcow2

Emulated/Virtualized environment

• Operating system: Haiku r1~beta4_hrev57383
• OS/kernel version: Haiku shredder 1 hrev57383 Nov 16 2023 07:32:15 x86_64 x86_64 Haiku
• Architecture: amd64

Description of problem

Documentation (such as https://www.qemu.org/docs/master/system/qemu-manpage.html or https://www.qemu.org/docs/master/system/devices/usb.html) says that enabling a USB keyboard or mouse (or tablet) will disable the PS/2 equivalent, but it seems both are present instead.

Steps to reproduce

1. Pass a -usbdevice or -device option to QEMU.
2. Boot Haiku.
3. Find two identical devices in Preferences > Input, both Extended PS/2 Mouse 1 and USB Tablet 1, as well as AT Keyboard 1 and USB Keyboard 1.

Additional information

The content of /var/log/syslog, which shows discovery of PS/2 devices: syslog.zst