I was wondering if anyone else was having this issue. It's been affecting both my single player and server. I noticed that in the SSP config file there are two options for generating tin and copper, so I made sure to set both to false. But after about 3 separate worlds being botched by this, I'm kinda at a loss. Definitely not a simple "forgot to save the config" error.
It's made much worse by the fact that I find playing with multiple types of the same ore to be unbearable.