[c-nsp] Adding vlan to port-channel trunk causes port-channel to flap

[Jared Gillis]

Hi all,

I just ran into a strange problem on a 3750ME. I've got two gig ports in an active LACP port-channel looking like this:

interface GigabitEthernet1/0/1
 switchport trunk encapsulation dot1q
 switchport trunk allowed vlan 101,102,400,664,1000-2999
 switchport mode trunk
 speed 1000
 duplex full
 channel-group 1 mode active
end

interface GigabitEthernet1/0/2
 switchport trunk encapsulation dot1q
 switchport trunk allowed vlan 101,102,400,664,1000-2999
 switchport mode trunk
 speed 1000
 duplex full
 channel-group 1 mode active
end

interface Port-channel1
 switchport trunk encapsulation dot1q
 switchport trunk allowed vlan 101,102,400,664,1000-2999
 switchport mode trunk
end

When I added vlan 400 to the trunk allowed vlan list, one of the underlying gig ports flapped, which caused the port-channel to flap as well. 
Jan  7 12:09:27.647 PST: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/1, changed state to down
Jan  7 12:09:27.656 PST: %LINEPROTO-5-UPDOWN: Line protocol on Interface Port-channel1, changed state to down
Jan  7 12:09:28.654 PST: %LINK-3-UPDOWN: Interface Port-channel1, changed state to down
Jan  7 12:09:31.464 PST: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/1, changed state to up
Jan  7 12:09:32.454 PST: %LINK-3-UPDOWN: Interface Port-channel1, changed state to up
Jan  7 12:09:33.461 PST: %LINEPROTO-5-UPDOWN: Line protocol on Interface Port-channel1, changed state to up
Jan  7 12:09:48.745 PST: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan400, changed state to up

This definitely seems like something that should not happen. I'm running Cisco IOS Software, C3750ME Software (C3750ME-I5K91-M), Version 12.2(46)SE, RELEASE SOFTWARE (fc2).
Any thoughts on what I should be checking?

--Jared