Hi there, I finally understand it, sorry for my slowness!
Last time a recorded a disc and used the "verify" option, then I got:
I 22:23:33 Device MD5: MD5 hash value 'A'
I 22:23:33 Device (Padded) MD5: MD5 hash value 'B'
I 22:23:33 Image MD5: MD5 hash value 'A'
In the end, imgburn says it matches but padded, I guess it's because that need to be divisible by 16 it increases the used sectors giving a different hash.