That's an odd problem. Does it actually cycle through each tab until it gets to the last one? If so, I know that rolling the mouse wheel when you are in the ribbon will cycle through the tabs similarly, so that makes me wonder if you have something odd happening with your mouse.
My first suggestion would be to reboot the computer to try to get rid of the "glitch". Second would be to try a different mouse to see if its something hardware related to the mouse. Third suggestion, chunk a brick at it...the bigger the better!!!