File Backups also appear to rely on absolute sector mapping for some reason

I realise that disk and partition backups map data blocks to absolute positions on the disk, and that is the reason why if you do an incremental backup immediately after having done a restore, or after having done a defrag, the incremental backup file will be big. (Actually, if True Image was capable of deduplication this wouldn't be a problem, but anyway....)

But here's the thing that's really perplexing: It seems that file backups are affected by this same limitation too.

I do a daily incremental file backup of some files I have stored on a drive attached to my router. Yesterday I rebooted the router during the day, and so when it came back online it re-mapped the drive and made it available as a network share again.

Looking at the backup set on my PC, I see that the incremental backup that ran yesterday evening was the same size as a full backup. Look at the last file in this list:

Software_full_b7_s1_v1.tib, 6,066,163,712 bytes, 31/03/2013 19:41:38
Software_inc_b7_s2_v1.tib, 28,672 bytes, 01/04/2013 19:30:37
Software_inc_b7_s3_v1.tib, 35,430,400 bytes, 02/04/2013 19:30:42
Software_inc_b7_s4_v1.tib, 669,827,072 bytes, 03/04/2013 19:32:28
Software_inc_b7_s5_v1.tib, 673,292,288 bytes, 04/04/2013 19:32:01
Software_inc_b7_s6_v1.tib, 907,001,856 bytes, 05/04/2013 19:32:21
Software_inc_b7_s7_v1.tib, 13,946,880 bytes, 06/04/2013 19:30:37
Software_inc_b7_s8_v1.tib, 32,768 bytes, 07/04/2013 19:30:37
Software_inc_b7_s9_v1.tib, 32,768 bytes, 08/04/2013 19:30:38
Software_inc_b7_s10_v1.tib, 436,088,832 bytes, 09/04/2013 19:31:27
Software_inc_b7_s11_v1.tib, 6,795,964,416 bytes, 10/04/2013 19:43:24

That is crazy. The only reason I can think of is that True Image somehow saw the entire file set as being at a different "absolute" position, and therefore backed up everything again, even though it should have just been incremental.

Can anyone explain this? Is there a good reason for that?