I had problems with my D800 since the begining. Taking picture in cold weather was sometime enfind with a "locked shutter". I had to trigger a second time to get things back in order. This was happening whatever lense I use, and putting these lenses on my D700 at the same time never triggered the issue.
I finaly sent back the B800 to Nikon support for repair. The D800 was shipped back the next day with a "no problem found" status.
Went out for shooting today (12 degres celcius) and the shutter problem is STILL HERE, even worse !!