I've just received my replacement from Logitech, and it appears to have no bad buttons. So, a happy ending for me, but I am left with a shattered sense of trust in Amazon, with whom I've been doing business since Day One, and deep skepticism about any Logitech product. These companies both need to stand up to this problem rather than try to wiggle around it as they are obviously doing. Containment is no longer possible in the Internet era; you would think these guys would understand that.

I assume this problem has been corrected at the manufacturing level, and the defective units will work their way through the supply chain over time, so my advice to any prospective buyer would be to wait a month or two, and then purchase from a high-volume source.