Problem removing netns

I am experimenting with netns (Linux precision 3.2.0-0.bpo.2-amd64 #1
SMP Sun Jun 3 21:40:57 UTC 2012 x86_64 GNU/Linux)
and have problems removing unused namespace, this is what I do:

ip netns add netns_one
ip netns add netns_two
ip link add name if_one type veth peer name if_one_peer
ip link add name if_two type veth peer name if_two_peer
ip link set dev if_one_peer netns netns_one
ip link set dev if_two_peer netns netns_two

ip netns exec netns_one bash

# in other terminal:

ip netns delete netns_two

# => Cannot remove /var/run/netns/netns_two: Device or resource busy

Is this expected  behaviour? If so, what is the correct process to
actually remove a namespace?

-- 
Bj(/)rnar