Maybe it wasn't cold enough in Siberia so they picked YFB instead, where the A380 itself did cold weather testing before it was certified. I recall at that time they said it wasn't quite as cold as they were hoping for.
Quoting ahlfors (Reply 2): Well, it has three engines covered and one uncovered, so maybe.
Well that answers it Cold weather testing for the TrentXWB.
Airbus has been to YFB for cold weather campaigns before. The A330F has been there as well as the A380, not sure about the A400M. Seems like a popular place for cold weather testing at Airbus.