Sometimes I found it funny to see even mods to find something "new" features. I've experienced that exactly same feature of "Nero switches speed while burning" sometimes. If you're using bad or low rated media, you may even see multiple messages of Nero switching to lower speeds.
First time I experienced this was with media which was rated at 40x, but finally burned at 16x. As that CD was quite well readable with old CD-drive I made it for, I paid no attention to that feature afterwards... but it was interesting to see!
Edit: LA, your sig is like made for me!