Do you see on top of the screen something that says "Tracking" and names or phrases follow?
It is yahoo telling you that the current fad on their search engine is whatever they list up top.
That will definitely do the up/down screen motions, making selection of a mail item impossible, like you say.
I consider it malware. Yahoo considers it a great feature to tell me the popular search words.
See this: http://www.bleepingcomputer.com/forums/topic361104.html
Edited by tos226, 08 March 2011 - 08:39 PM.