I managed to get this lab to work correctly with GNS3 1.5.2 and below IOS´s
DHCPv6#
BOOTLDR: 7200 Software (C7200-ADVIPSERVICESK9-M), Version 15.2(4)S5, RELEASE SOFTWARE (fc1)
CLIENT_1#
BOOTLDR: 7200 Software (C7200-ADVENTERPRISEK9-M), Version 12.4(24)T5, RELEASE SOFTWARE (fc3)
CLIENT_2#
BOOTLDR: 7200 Software (C7200-ADVIPSERVICESK9-M), Version 15.2(4)S5, RELEASE SOFTWARE (fc1)