The default thumbwheel direction is wrong - it's incompatible with the 'standard' scrollwheel direction.
The standard scrollwheel 'down' (pull the wheel towards person) moves the viewport down over the document. But the thumbwheel 'right' (roll the wheel clockwise) moves the viewport to the left. It's instead moving the document under the viewport instead of moving the viewport over the document. The mouse (and trackpad) should be viewport-oriented, not document oriented (IMHO)