I experience this problem too. In my case, I'm running Debian 12.9 and using virt-manager to view the VNC console of the VM.
I don't know who should own the bug, but I have also filed a bug report on pixman, where I included details of my findings. It appears to be an out-of-bounds memory access on the source buffer, possibly in function arm_neon_blt. https://gitlab.freedesktop.org/pixman/pixman/-/issues/119 I was able to work around the problem by removing the Spice display from my VM. My VM had both Spice and VNC displays. Even though I was using VNC, the presence of the Spice display seemed to cause the problem.
