Symptom:
The backplane serial number will show up wrong in show idprom backplane cli output. The primary and secondary serial number will be shown swapped in the output

Conditions:
Router#sh idprom back det
IDPROM for backplane #0
IDPROM image:

  (FRU is 'Catalyst 6807 7-slot backplane')

IDPROM image block #0:

  block-signature = 0xABAB, block-version = 4,
  block-length = 178, block-checksum = 5471

  *** common-block ***
  IDPROM capacity (bytes) = 512  IDPROM block-count = 2
  FRU Major Type = '0x6001'
  FRU Minor Type = '0x7001'
  OEM String = 'Cisco Systems, Inc.'
  Product Number = 'C6807-XL'
  Serial Number = 'SMC1732304Y'  <<<<<<< THIS IS SECONDARY
  Manufacturing Assembly Number = '73-15269-03'
  Manufacturing Assembly Revision = '02'
  Manufacturing Assembly Deviation = ''
  Hardware Revision = 0.302
  Manufacturing bits = 0x0  Engineering bits = 0x0
  SNMP OID = 9.12.3.1.3.1305
  Power Consumption = -286 centiamperes    RMA failure code = 0-0-0-0
  CLEI =
  VID =
  RFID =
  *** end of common block ***

IDPROM image block #1:

  block-signature = 0x6001, block-version = 4,
  block-length = 77, block-checksum = 1869
  *** backplane specific block ***
  feature-bits =  0x00000000 00000000
  hardware-changes-bits =   0x00000000 00000004
  stackmib-oid = 55
  mac base = D0C7.89A8.08C0
  mac_len = 64
  OEM Enterprise = 9
  OEM MIB Offset = 5
  Max connector power = 0
  Cooling Coefficient = 0
  Chassis RFID =
  Secondary Serial Number = 'SMC1740000C' <<<<< THIS IS THE PRIMARY
  *** end of backplane specific block ***