I've received my four and they seem to be working ok, but they are dying occasionally. Like this morning two of three I have plugged into one comp were just not hashing, but had been working for the whole day while I was awake yesterday. When I restart bfgminer they're working fine though. Is this related to using higher frequency? Higher frequency without tuning voltage? Computer not splitting enough current? Something else?
Did you change from stock setting? You get zombie state if USB port can't provide enough amperage. On multiple devices, if one device acts up, that can't affect the other ones. Single stock is most stable but multi stock you should expect them to zombie hopefully later than sooner.
I did increase clock frequency to 700-something. Two are plugged directly into mobo and one in USB on front side of comp. I'll try to go back to stick and see if they can work uninterrupted for couple days at least. This is on Windows 7 computer.