The 5500 manual says one shouldn't use VLAN 1 on access ports. Furthermore, it couldn't be added to trunk ports.
Unfortunately, the manual gives no reason. Normally, all VLANs are tagged on trunk ports. Is VLAN 1 not tagged? Is VLAN 1 then local to a switch only?
Isn't it possible to leave VLAN 1 on all access ports untagged and forward it tagged on the trunks?