I understand this but there is one problem - in original CPU miner from Neisklar (https://github.com/Neisklar/quarkcoin-cpuminer) I am pretty sure diff1 is set the same as sha256 and it is used by thousands of users...
It used to be that the Neisklar miner was hardcoded to never submit shares below a certain difficulty, which masked the problem. This was fixed 7 months ago. Not sure if that is related to this issue?