device_add usb-hub causes segfault in qemu-1.0

When calling the command

(qemu) device_add usb-hub,bus=usb.0,port=4

qemu replies

Error: usb port 4 (bus usb.0) not found (in use?)

Then qemu crashes with a segfault:

[ 1546.177627] qemu-system-x86[1710]: segfault at 0 ip b75d3f8b sp bfddb0b0 error 6 in qemu-system-x86_64[b7488000+2e2000]

Maybe it might be related to the docs/usb2.txt where UHCI has only 2 ports. But a mistake in the port number should not cause qemu to crash