[virt-tools-list] black screen with qemu/qxl/virt-viewer after world update

[email200202]

My setup is app-emulation/qemu-4.0.0-r50, net-misc/spice-gtk-0.37-r2, 
and x11-drivers/xf86-video-qxl-0.1.5. The VM and the host are both 
~amd64 Gentoo Linux.

The startup script:
qemu-system-x86_64 --enable-kvm -daemonize \
-name ${NAME} \
-machine type=pc,accel=kvm \
-cpu host \
-smp 2 \
-vga none -device qxl-vga,vgamem_mb=32 \
${CDROM} \
${DRIVEA} ${DRIVEB} \
-m 2G \
-soundhw ac97 \
-device usb-tablet \
-device virtio-balloon \
-netdev tap,id=net0,script=/root/qemu-ifup \
-device virtio-net-pci,netdev=net0,mac=${MAC_ADDR} \
-usb \
-device ich9-usb-ehci1,id=usb \
-device ich9-usb-uhci1,masterbus=usb.0,firstport=0,multifunction=on \
-device ich9-usb-uhci2,masterbus=usb.0,firstport=2 \
-device ich9-usb-uhci3,masterbus=usb.0,firstport=4 \
-chardev spicevmc,name=usbredir,id=usbredirchardev1 \
-device usb-redir,chardev=usbredirchardev1,id=usbredirdev1 \
-chardev spicevmc,name=usbredir,id=usbredirchardev2 \
-device usb-redir,chardev=usbredirchardev2,id=usbredirdev2 \
-chardev spicevmc,name=usbredir,id=usbredirchardev3 \
-device usb-redir,chardev=usbredirchardev3,id=usbredirdev3 \
-spice port=${SPICE_PORT},addr=127.0.0.1,disable-ticketing \
-device virtio-serial-pci \
-device virtserialport,chardev=spicechannel0,name=com.redhat.spice.0 \
-chardev spicevmc,id=spicechannel0,name=vdagent \

The spicy command:
spicy --title ${NAME} -p ${SPICE_PORT}

It was working for more than 10 months. The problem developed in the 
last two days after gentoo 'world' update.

The VM boots normally but after X starts the VM display becomes black 
with the "session" in the middle (see the attached snapshot). I can 
still login to the VM using ssh.

virt-viewer gave me the same results as spicy.

I tried to upgrade/downgrade all the relevant packages but I couldn't 
find which package update caused the problem.

Any ideas?