What blocks MD5SUM / SHA256SUM calculations?

I have something of a puzzle. On a certain distro I can find the hashes for the iso file, but when I burn it to a cd, the only response I get is: "Input - Output error"

There is nothing wrong with the drive, I can verify the hashes on any other CD or DVD without fail. If it was a bad disk, I would expect to see the wrong hash, but not the results I"m getting.

Has anyone experienced this, or have related information?

I've had times when I burn a disk with K3B, and it claims to be bad when its verifying writtten data but they were always good. No idea what causes it though.

I found something on the forum about the cause being empty blocks left over after the burn. There was a solution suggested, but I want to try it out before posting it here.

When the published MD5 hash does not include the padding to fill the CD, there is a discrepancy between the published and md5sum hashes. This does not necessarily indicate a bad burn.
This command will provide the correct information:
[laz@GA-P55A-UD6 ~]$ dd if=/dev/sr0 bs=2k count=$(($(isosize /dev/sr0)/2048)) | md5sum
221077+0 records in
221077+0 records out
452765696 bytes (453 MB) copied, 101.34 s, 4.5 MB/s

ddf1f95e532dae8794532c31fa3ecaeb -
Now we have a match.