Lxc-device add and del devices repeatedly,permission changed

LXC version:3.2.1

1. First show my config:

# CGroup whitelist
lxc.cgroup.devices.deny = a
## Allow any mknod (but not reading/writing the node)
lxc.cgroup.devices.allow = c *:* m
lxc.cgroup.devices.allow = b *:* m

I have not give allow to device “c 248:2 rwm” --> /dev/ttyO2

2. Then I create and start my container named test2

3. after container running I add /dev/ttyO2 to test2

# lxc-device -n test2 add /dev/ttyO2

4.test2 should not allow to open /dev/ttyO2,but it can be open

5. Then i del /dev/ttyO2 to test2 from test2

# lxc-device -n test2 del /dev/ttyO2

6. Then add it again

# lxc-device -n test2 add /dev/ttyO2

7. Then open /dev/ttyO2 in container test2 again return "Operation not permitted"

Result :first add /dev/ttyO2,the permission is allow,then del and add again ,the permission is deny