How to prevent middle mouse button from activating the application switcher

Ah ha! I found the solution. The problem stems from the mouse settings from way back when I had an Apple Might Mouse (the one with the pea sized scroll ball in the centre). When the Mighty Mouse is plugged in, extra options appear in System Preferences > Mouse. There are pull downs for assigning commands to the side (squeeze) buttons, and the scroll ball click! I had mine setup for Application Switcher!

I can't believe that the only way to change this setting is to have a Mighty Mouse plugged in! Good thing I just happened to have one lying around!

Mouse settings when only the third party mouse is plugged in:

With the Mighty Mouse also plugged in:

I don't see anything in the Mouse or Mission Control system preferences that would trigger the Application Switcher from a mouse button click.