This is my experience...may not be yours.
I use Kprobe to check my dvd burns. I have noticed this on some of Ridata matte printables (G04's)....junk media...yes, junk. The Ritek 4x I have used have a PI/PO error that is very high over 4gb (or so). I've thrown out some unburned silver tops and most of these printables already. Please, if you're a "Ritekie", spare me the "I've burned 2 million Riteks without a coaster" comments. I've never "burned" a coaster either...only tested them as such. I am not a Ritek expert...can't afford it...I've wasted enough time and money on the silver tops and printables. Other types may be fine...I am impressed with the low PI/PO error on the good parts.
Anyway, here is a 3.7gb burn on my A06, f/w 1.07 hacked (note: I have slightly higher, but similar results with my Liteon, which is on a totally different system):
Normally, this would constitute a good disk...In my case, it's crap. See this (ignore the vertical lines - shadows..I have a suggy old scanner):
My older GE standalone chokes like a gloryhole first-timer at that location. Notice the die thinning (dark circular band)...Kprobe shows PI error rising slightly at this location. The funny thing is that the dvd plays fine at the end (where the PI error is about the same). My standalone is picky about media, but not this picky.
I guess what I'm trying to say is: Kprobe is a good quick check, but the only true way to tell is to watch it on your standalone. Also, a close visual check of your media before and after you burn wouldn't hurt.