Well, from personal experience I can say it doesn't always turn out that way. I suffer from the same problem you see
It's the only reason I've ceased to use Nero as my main burning software. It's a bit of a pain using Alcohol 120% since I have to make an ISO with seperate software, but at least I can count on the software!
the scary thing is: I've compared burn quality from Nero to alcohol 120% and there is usually a significant difference between the two!! (meaning alcohol 120% usually performs better). It may just be because of the Nero bug, but it deffinatly surprised me.
I'll see if I can re-create the problem and link some screenshots from my webpage later.