I know this is an old thread but I just wanted to respond to my experience regarding this to help out others
When I bought my 328i as a Demo (was in service for about 8 months), the driver's side mirror was chipped in the same place, but not cracked across. Asked the dealer to replace it, they told me their "warranty" guy (who knew there was such guy...) said BMW probably wouldn't cover it and to claim it under insurance. Told them to take the equivalent of the comprehensive deductible $ amount off the sale price which they hesitantly did.
Fast forward about 2 months, went to another BMW dealer given that the original selling BMW dealer wouldn't cover it. They gladly told me they would cover it under warranty. So just got it replaced under warranty today, since the original replacement was also chipped but on two leading edges... Shows how durable the high gloss shadow line trim is.
So moral of the story, its defective and should be easily a warranty item!