odd dvd-r burning pattern

[spiritgumm]

I'm having a weird burn on dvd-r (happened on one HP dvd, and on several TDK dvds). I don't know what brand burner I have.
If you burn a a short movie on a dvd, you can see the contrast between the burned (darkened) area versus the outer unburned area. I'm getting a tiny smudge of unburnedness in the burned area (imagine a fingertip placed on a fogged over bathroom mirror). These discs play fine on a player, and read/copy fine in a computer. Does anyone know what this is? Is it a problem?

[boss]

on all the dvd's i have burned you can see the contrast as well. but i think this is normal(you can see it on some pressed cd's as well)
but i also have little smudges in the burned areas. which i worry about. some of them are there because there was some dirt on the dvd. so make sure the discs are clean before you burn them. but i also have some tiny unburned areas on dvd's that were clean as well. could this be due to a problem with the media?

[spiritgumm]

I know the contrast between burned/unburned area is normal. The point I was making is that the lightness of the smudge in the burned area resembles the unburned area - implying that it wasn't burned correctly. Yet it plays, etc., for now...
I always check discs before putting them into a machine, and never saw any dirt, etc., prior to burning.