It's not the shared borders thing.The only guess I have is that maybe the font you're using for your navigation buttons in your theme is not comming through. I notice that some of the words on the nav buttons are too long for the buttons.
If that font is installed on your machine then you should be able to just open your live site > format > theme > modify > graphics > vertical navigation > set the font.
If that font is not on your machine, then you have to pick one that is or get that font.