Since using zoom:1 fixed the problem in the code I originally posted but did not fix the problem in my actual code, here's another version that is closer to my actual code (it has been difficult to narrow down the cause of the problem and I suspect there may be more than one cause).
http://jsfiddle.net/yWe2C/7/ I used zoom:1 as suggested by Thomas, and moved the styles from the javascript code to the stylesheet as suggested by Gafa. If you move the mouse quickly into the "Title" div from the right hand side, while keeping the mouse away from the "Title" text, you will see the mouseenter event fail to fire. The major difference between the code I originally posted and this code is the presence of the "header" div.
