Your menu does not look and behave the same as my menu on my test site.
Are you using custom css for your menu in 2.6.4?
If yes, I suggest you to remove it and use what’s available in Theme Options -> Styling -> Menu
the mouse over will ‘slide up’ the menu instead of just flash it.
Sorry, I do not understand this. Maybe you are referring to the menu item animation.
You can go to Theme Options -> Header -> Menu -> Choose menu item hover effect
To choose your effect or turn it off.