My only concern here is the sudden unannounced change. If CCP had either communicated or they had gradually reduced the yields - say 1 or 2 percent per day, then this would have been fine. But to make people wonder if it is a bug in the code, does not speak well of CCP, given the issues that already exist in the code base.
I understand the reasoning, not sure if it will solve the problems that CCP perceives exist.
I for one have a lot of unrefined ore siting in a station, because when I have a day off of work, I mine all day, just to have no-brains required activity. From a brain activity point of view, I treat it as human run boting.
It means my activities over the holidays may actually be worth something, while I relax and stop having to think so hard mining.
But CCP - either gradually or announce it in the future.