My machine has software raid:

[root@gnu-3 boot]# blkid
/dev/sda: TYPE="promise_fasttrack_raid_member" 
/dev/sdb: TYPE="promise_fasttrack_raid_member" 
/dev/mapper/pdc_biehcghfjcp8: UUID="c45758b7-0d71-4137-97f4-abff9f596457" TYPE="swap" 
/dev/mapper/pdc_biehcghfjcp9: UUID="1b4b961f-7beb-4107-8d3c-ea6fc4a4aada" TYPE="ext4" 
/dev/dm-12: LABEL="/export" UUID="2e53fbaf-1a07-4eb6-82b3-f6c737471593" TYPE="ext3" 
/dev/dm-1: UUID="a1893a01-c609-4dc7-8deb-eeeafc279bff" TYPE="ext4" 
/dev/dm-10: UUID="2889dff3-124c-4314-81af-5dd3e1d7c675" TYPE="ext4" 
/dev/dm-2: UUID="4ac784f2-e01d-423a-ad7f-8f5d2581d14b" TYPE="ext3" 
/dev/dm-3: UUID="0cbe36c6-2206-4bd2-ac13-1cf4672d612b" TYPE="ext4" 
/dev/dm-5: UUID="85f23229-dd96-447e-8d13-d05386434456" TYPE="ext4" 
/dev/dm-6: UUID="5f77b5e3-948c-4527-b2af-1b3757fc28c3" TYPE="ext3" 
/dev/dm-7: UUID="d6634e3d-c7d3-4319-83d0-a36dc5c49f10" TYPE="ext4" 
/dev/dm-9: UUID="1b4b961f-7beb-4107-8d3c-ea6fc4a4aada" TYPE="ext4" 
[root@gnu-3 boot]# dmraid -s -c
ERROR: ddf1: seeking device "/dev/dm-4" to 18446744073709421056
ERROR: hpt37x: seeking device "/dev/dm-4" to 4608
ERROR: hpt45x: seeking device "/dev/dm-4" to 18446744073709547008
ERROR: pdc: seeking device "/dev/dm-4" to 137438913024
ERROR: pdc: seeking device "/dev/dm-4" to 137438920192
ERROR: pdc: seeking device "/dev/dm-4" to 137438927360
ERROR: pdc: seeking device "/dev/dm-4" to 137438934528
ERROR: sil: seeking device "/dev/dm-4" to 18446744073709289984
pdc_bigbhfbaei
pdc_biehcghfjc
[root@gnu-3 boot]# ls /dev/mapper/
control         pdc_biehcghfjcp1   pdc_biehcghfjcp2  pdc_biehcghfjcp4  pdc_biehcghfjcp6  pdc_biehcghfjcp8  pdc_bigbhfbaei
pdc_biehcghfjc  pdc_biehcghfjcp10  pdc_biehcghfjcp3  pdc_biehcghfjcp5  pdc_biehcghfjcp7  pdc_biehcghfjcp9  pdc_bigbhfbaeip1
[root@gnu-3 boot]# 

pdc_biehcghfjcp4 (aka "/dev/dm-4") is the extended partition.

/bin/os-prober has

set -e
...
for partition in $(partitions); do
...
  type=$(blkid -o value -s TYPE $mapped)
...
done

We got

[root@gnu-3 boot]# blkid -o value -s TYPE /dev/dm-1
ext4
[root@gnu-3 boot]# blkid -o value -s TYPE /dev/dm-4
[root@gnu-3 boot]# echo $?
2
[root@gnu-3 boot]# 

Due to "set -e", blkid -o value -s TYPE /dev/dm-4 will
terminate the FOR loop and skip the rest of partitions.

Change

type=$(blkid -o value -s TYPE $mapped)

to

type=$(blkid -o value -s TYPE $mapped || true)

fixes the problem.