Strange Reading With Nero and my DVD-R Media

If any of you have Nero your probably familiar with it's ScanDisc feature it has in its tool box. This allows you to scan the integrity of your media with a File Test and a Surface Scan.

I was testing a stack off all DVD-Rs I had burned a few months back when I got a strange result on the very last one.

The first scan (done in my bottom Mad Dog DL DVD+-RW burner) came back with the following results:

Errors: 2
Readable Sectors: 99.3%
Unreadable Sectors: .70%

I then place the same DVD-R in the top burner (also an identical model Mad Dog DL DVD+-RW burner) and got a clean reading:

Errors: 0
Readable Sectors: 100%
Unreadable Sectors: 0%

This puzzled me so I took the disc out, cleaned it and put it back in the drive I did the scan in originally (the bottom Mad Dog burner) and, again got the original error reading:

Errors: 2
Readable Sectors: 99.3%
Unreadable Sectors: .70%

Any reason why two identical model burners setup exactly the same would get two different readings for the same disc? Could it be a faulty drive?