A1 drives itself - how is this right ?

I have an '11 plate Competition Line A1 with no cruise control function and yet at random times it keeps the speed when I take my foot off the pedal and even increases speed despite going, sometimes, uphill! East Kent Audi have told me this is normal for a diesel. They investigated and found nothing abnormal but told me diesel engines do this and when they test drove it, it didn't happen yet on the drive home it happened twice. My friends who have diesels don't report this. Can this be right? I sometimes feel that I am trying to pull it back like a horse on reins and not until I change gear does it slow.