I'm guessing you have touchpad corners enabled. Usually by default lower-right is 2nd mouse button and upper-right is 3rd mouse button (middle click).

I only use the touchpad, but knowing where it is I can avoid it and almost never trigger it accidentally. It can also be disabled without affecting two-finger and three-finger tap, which I do use.

(This applies to all laptops, not just Thinkpads)

> I'm guessing you have touchpad corners enabled.

Er, no. As I said:

Usually I leave the trackpad disabled. I don't like gestures and multi-finger taps much so I prefer to just turn it off.