I've been mining with cex.io for about a week and I'm seeing VERY high stale counts for my ghash.io account and very high duplicate counts for my KNC miner. Overall the performance is what I expected but I'm wondering if there is anything I can/should do about the high stale and duplicate counts??!!
I've read about this problem with KnC hardware, and it's most likely harmless. Only thing that matters is how many valid shares you end up sending to the pool. IIRC the firmware just doesn't clear its results sometimes, so cgminer thinks the same old result is a new one. No work is wasted when that share is sent again, but it ends up in the duplicate statistics.