[CentOS] C7 Backup problem

Good morning list,
I've a question about backup performed with bacula.
I manage a DELL server (dedicated on provider) with C7. I use bacula as 
backup system with volumes on disk. System performs mon-sat incremental 
backups and Sun full backup at 03.00 AM. I've another pool (named 
update) where I performs backup before each software update. Storage is 
on and external disk 2.5' of 1TB.

Yesterday, I've applied centos update and I've performed a full backup 
before apply updates. Job done.

After several hours, I got my disk unmounted and disconnected due to 
disk error (seems that this disk is failing) and was unable to remount 
disk. Rebooting system, the disk was mounted correctly.

This morning I've checked if something happened. Backup performed and 
disk mounted without errors but I've noticed a strange behaviour.

My incremental backup is large as last full backup (performed on 
sunday). This is the last jobs performed.

   76 | backup-fd | 2016-08-07 03:04:44 | B    | F     |  191,040 | 
7,975,649,059 | T         |
|    77 | backup-fd | 2016-08-08 03:04:57 | B    | I     |       44 | 
44,593,988 | T         | 
 

|    78 | backup-fd | 2016-08-08 09:52:57 | B    | F     |  191,024 | 
7,978,295,072 | T         | 
 

|    79 | backup-fd | 2016-08-08 12:10:31 | B    | F     |        0 | 
          0 | A         | 
 

|    80 | backup-fd | 2016-08-09 03:05:03 | B    | I     |  191,024 | 
7,978,337,100 | T


Job with id 79 was aborted due to disk failure.

Why, if I have a job full performed on sunday, on monday I got an incr 
job with the same size? Seems to be that the last incremental job was 
performed without considering the last full backup.

I've checked log but there aren't errors.

Thanks.

Alessandro.