This is not a bug but a specification of eucalyptus currently.
Therefore, once I had surrendered the MANAGED mode in building eucalyptus at a data center concerning this issue.
The center could provide a certain range of VLAN tags and a limited subnet for the system, then eucalyptus could not use them.
I think the case like this is not so rare.
I wish VLAN tag numberings and the size of subnet become decoupled like Daniel said.