Well i'm not sure that adding/removing vlans from port-channel automaticaly adds coresponding commands to its members...i think that you need to do that by your own on that members...but again thats straight out of head - didn't tested...
For your other constraint (that only one device behaves wrongly) could you post adequate configurations? I think that there must be something different.
HTH,
Dragan
HTH,
Dragan