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RHEL-7 qemu should do tghis correctly, patch is upstream.

verify this issue on qemu-kvm-1.5.1-2.el7.x86_64, the QEMU did not core dump and will prompt that the device 'usb-ehci'|'nec-usb-xhci' does not support hotplugging. 
But for there is still prompt that 'An undefined error has occurred', please refer to existing bug 949211. 
host info:
3.10.0-0.rc7.64.el7.x86_64
qemu-kvm-1.5.1-2.el7.x86_64
guest info:
3.10.0-0.rc7.64.el7.x86_64

# /usr/libexec/qemu-kvm -M pc-i440fx-rhel7.0.0 ....-device nec-usb-xhci,id=xhci,bus=pci.0,addr=0x8 -device usb-ehci,id=ehci,bus=pci.0,addr=0x9
(qemu) device_del ehci
Device 'usb-ehci' does not support hotplugging
An undefined error has occurred
(qemu) device_del xhci
Device 'nec-usb-xhci' does not support hotplugging
An undefined error has occurred

Base on above, this issue has been fixed, set to verified status. please correct me if any mistake.

Best Regards,
sluo

This request was resolved in Red Hat Enterprise Linux 7.0.

Contact your manager or support representative in case you have further questions about the request.