解决方法
这是Bug.
Issue 336348:Last option of select does not get highlighted on mouse hover
并且还看到Issue 334227:[Aura] Regression : Last dropdown item not highlighted on mouse-hover
It’s not the problem with your code it’s due to Google Chrome Bug.
With more than 3 options this bug comes into play.
此问题已在Google Chrome最新版本32.0.1700.102 m中修复.
Solution Update your Google Chrome to latest Version.
