using libvirt 4.5 with upstream qemu

I'm trying to use QEMU master with libvirt 4.5 and QEMU seems to be hanging when I try to start a guest. My environment is a modified CentOS 7.9 installation using libvirt 4.5.0. When I use a modified version of QEMU 2.12 (reasonably close to the stock CentOS version) everything works fine. When I try to use a fairly recent version of QEMU (e.g. v5.2.0-729-g89ff714f4b). qemu 118657 1.6 0.0 0 0 ? Z 14:50 0:00 [qemu-kvm] <defunct> qemu 118664 0.0 0.0 207340 3560 ? Ssl 14:50 0:00 /usr/libexec/qemu-kvm -S -no-user-config -nodefaults -nographic -machine none,accel=kvm:tcg -qmp unix:/var/lib/libvirt/qemu/capabilities.monitor.sock,server,nowait -pidfile /var/lib/libvirt/qemu/capabilities.pidfile -daemonize qemu 118666 0.0 0.0 275008 13916 ? Sl 14:50 0:00 /usr/libexec/qemu-kvm -S -no-user-config -nodefaults -nographic -machine none,accel=kvm:tcg -qmp unix:/var/lib/libvirt/qemu/capabilities.monitor.sock,server,nowait -pidfile /var/lib/libvirt/qemu/capabilities.pidfile -daemonize /var/lib/libvirt/qemu/capabilities.pidfile contains the PID of the 2nd QEMU process and by experimenting I found that by killing the QEMU process NOT in the PID file the same thing happens again (maybe once more or twice) and then the guest boots fine. Does libvirt have some specific QEMU dependency? Is there some compatibility matrix I might have missed? I understand this may not be a supported configuration given that I'm not using vanilla libvirt/QEMU, however I'd appreciate some pointers so I can further debug this. I've trying debugging this in case there's some obvious error but didn't find anything interesting. Any ideas?