Nokia's firmware changing bluetooth mac address

I own a Nokia X6 16Gb, and the other day, software update remind me that a new version is ready for download.

I download and install it, and after that, I realise that bluetooth's mac address was changed!

Weird but true. The version is 40.0.002, with date 12-10-2011.
Does anyone else has that experience?

Nokia, why is that?