I find it interesting that this little hiccup is now being discussed at length. I am a drummer too. I noticed the error too. I'm also an audio engineer and I know how to program drums. Adrian probably didn't quantise a few beats after hammering them into the MIDI track with a tap on the keyboard. Apart from the ONE error, everything else on the drum track is perfectly quantised. It is therefore a very obvious error that cannot be explained away, Adrian messed it up. But since it was only a demo, he didn't care! He's a guitarist after all. Steve then took the demo, probably heard the error too, but didn't care - I bet he didn't even think of it as something to be corrected *or* left in, he just never thought about touching the demo, and therefore the error.
I think it is kind of funny, since there have been *real* production errors on various metal records that are clearly the producer's fault. I also wish that this little error would have been corrected (would not have done any harm to the atmosphere of the track), as I think that if you do use a drum machine, you'd better do it right. But again, this was not a production error. It simply wasn't meant to be on the record. I don't really like it, but I understand why it's there. Still doesn't ruin either the track or the album for me!
Oh and Death on the Road was a huge disappointment once I watched it on my flatscreen TV. The picture quality is unbelievably low, it's not even real SD. *That* kills a Maiden release for me, not just some small glitch.