CDROM hotplug not supported even with usb bus

Hi, I am using libvirt-4.5.0 + qemu-kvm-ev-2.12.0 and I have a question about the cdrom function of libvirt. When I tried to attach a CD ROM, it rejected the operation showing "cdrom/floppy device hotplug isn't supported". I understand that it should be rejected when the IDE bus is used, but the hotplug with USB bus is totally feasible, as it's also supported in qemu, in this case, should it be allowed for hotplug? I have not tried the newest version of libvirt yet, but looking at the upstream source code it seems that there is no change regarding this issue. Thank you, Tianren Zhang