unable to add classes to a dsmark qdisc using 'add'

[samudrala@us.ibm.com]

why can't we add classes to a dsmark qdisc using 'add' command?

tc qdisc add dev eth1 handle 1:0 root dsmark indices 64 set_tc_index

After adding the above qdisc, when i try to add a class using the following
command, it fails.

tc class add dev eth1 parent 1:0 classid 1:1 dsmark mask 0x3 value 0xb8
RTNETLINK answers: File exists

But if i add a class using change command it works.

tc class change dev eth1 parent 1:0 classid 1:1 dsmark mask 0x3 value 0xb8

Is this a bug?  If not, what is the reason for this behaviour?

Thanks
Sridhar