layer 2 protocol tunneling with dvlan-tunnel (QinQ) on 6200 switch

When using dvlan-tunnelling (QinQ) on a 6224F switch it passes some layer 2 control frames (cisco CDP for example) but not STP frames.  It doesn't matter if STP is enabled or disabled (with STP flooding) on the 6200.  Am I missing something in the configuration, is this a bug or simply not possible on the 6200 platform?

In the lab I have a MPLS core, Dell switches at the edge and cisco switches for customer switches.  The cisco switches have an IP address in their default VLAN (VLAN1) and I can ping between them across the VPLS core.  If I move the cisco switches up to the PE devices, STP works between them.  In this case it appears the 6200's are eating the STP frames, and possibly other layer 2 control frames.  I'm expecting complete transparency when in tunnel mode. 

as0-site2#show run
!Current Configuration:
!System Description "Powerconnect 6224F, 3.2.0.7, VxWorks 6.5"
!System Software Version 3.2.0.7
!Cut-through mode is configured as disabled
!
configure
vlan database
vlan 2000-2010,3000-3010,3200-3210
exit
hostname "as0-site2"
stack
member 1 3
exit
switch 1 priority 12
ip address none
no isdp enable
no spanning-tree
spanning-tree bpdu flooding
!
interface ethernet 1/g21
description 'To Customer CE Switch'
mtu 9000
switchport mode general
switchport general pvid 2000
switchport general allowed vlan add 2000
exit
!
interface ethernet 1/g23
channel-group 1 mode on
mtu 9000
exit
!
interface ethernet 1/g24
channel-group 1 mode on
mtu 9000
exit
!
interface port-channel 1
description 'Uplink to MPLS backbone'
switchport mode trunk
switchport trunk allowed vlan add 2000-2010,3000-3010,3200-3210
mtu 9000
mode dvlan-tunnel
exit
exit

as0-site2#