vhost-user: can not detach chardev which is used by vhost-user backend

I launch a VM which use vhost-user netdevice as follows.When detach the netdevice in qemu monitor, the chardevice which used by the netdevice also should be deatched.The netdevice can be detached sucessfully.But the chardevice  failed when it was being detaching.   
Full command line :
qemu-system-x86_64 \
-cpu host -boot c -hda /home/lining/ubuntu_12_04.img -snapshot -m 2048 -smp 2 \
--enable-kvm -name "client1" -vnc :1 \
-object memory-backend-file,id=mem,size=2048M,mem-path=/dev/hugepages,share=on -numa node,memdev=mem \
-chardev socket,id=chr1,path=/opt/network/ovdk/bin/vhost-user \
-netdev vhost-user,id=net12,chardev=chr1,ifname=port80, vhostforce \
-device virtio-net-pci,netdev=net12,mac=00:00:00:00:00:01,\
csum=off,gso=off,guest_tso4=off,guest_tso6=off,guest_ecn=off,guest_ufo=off,any_layout=off