I have had a RFN-4s for several months and have noticed a problem on the D800 when shooting in BKT mode. It isn't consistent and locks up the camera requiring a full power down of the remote unit to clear. My experience suggests the problem is easier to reproduce when the number of bracket shots is a higher number like 5 or 7 instead of 3. I would be interested in hearing if anyone else can reproduce this issue.
Shooting single images has been fine and battery life on the remote has been excellent.