I think, it is the testing method: we all know (read the KProbe FAQ), that KProbe is no "absolute" tool but can just give you a tendency, where your quality of the burns go. It is all dependent on the hardware, you are using to test the burn.
So: you never know, how good the hardware actually is you are testing it with. I have seen scans of the VERY SAME burn done with different LiteOn-DVD-ROMs and some done with the SAME MODEL (different manufacturing dates), and they all were different.
In other words: I am not worried about that solid block of "1"s at all....
If I happen to find a scan of my old 811s, I'll post it, so you'll see.